support axis=None for nanmedian ( issue #7352 )
This fixes #7352, where `nanmedian` does not work when `axis==None`.

I have added a fix (hopefully) for the rounding errors
 thanks!
 @toddrjen a bunch of tests failing on windows. I debugged one of them below.

If you can debug this would be great.

```
C:\Users\Jeff Reback\Documents\GitHub\pandas>more test.27-64.log
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...................................................................C:\python27-64\lib\site-packages\numpy\core\_methods.py:55: RuntimeWarning: Mean of empty slice.
  warnings.warn("Mean of empty slice.", RuntimeWarning)
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...SS.....S...SS.......S.S.......................SS.....S...SS.......S.S..............SS..SS.......................................................................S....................................
.........................................C:\python27-64\lib\site-packages\matplotlib\axes.py:4747: UserWarning: No labeled objects found. Use label='...' kwarg on individual plots.
  warnings.warn("No labeled objects found. "
....................................................................................................................................................C:\python27-64\lib\site-packages\matplotlib\__init__
.py:1172: UserWarning:  This call to matplotlib.use() has no effect
because the backend has already been chosen;
matplotlib.use() must be called *before* pylab, matplotlib.pyplot,
or matplotlib.backends is imported for the first time.

  warnings.warn(_use_error_msg)
..............................................................................................................................................c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win
-amd64-2.7\pandas\core\index.py:1013: RuntimeWarning: Cannot compare type 'Timestamp' with type 'str', sort order is undefined for incomparable objects
  "incomparable objects" % e, RuntimeWarning)
..................................................c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\index.py:1013: RuntimeWarning: Cannot compare type 'Timestamp' with t
ype 'long', sort order is undefined for incomparable objects
  "incomparable objects" % e, RuntimeWarning)
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......................c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py:193: ComplexWarning: Casting complex values to real discards the imaginary part
  return ~np.isfinite(values.astype('float64'))
.............E..EE.E...E......................................................................................................................................S...S.............SSS.........S...........
.SS.............SS.....SSSS.............................................................................................................................................................................
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======================================================================
ERROR: test_nankurt (pandas.tests.test_nanops.TestnanopsDataFrame)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 373, in test_nankurt
    allow_complex=False, allow_str=False, allow_date=False)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 213, in check_funs
    self.check_fun(testfunc, targfunc, 'arr_float', **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 202, in check_fun
    testarval, targarval, targarnanval, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 160, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 43, in _f
    return f(*args, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 483, in nankurt
    count = _get_counts(mask, axis)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 542, in _get_counts
    count = (mask.shape[axis] - mask.sum(axis)).astype(float)
AttributeError: ("'long' object has no attribute 'astype'", 'axis: 0 of 0', 'skipna: False', 'kwargs: {}', 'testar: arr_float', 'targar: arr_float', 'targarnan: arr_float')

======================================================================
ERROR: test_nanmax (pandas.tests.test_nanops.TestnanopsDataFrame)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 320, in test_nanmax
    allow_str=False, allow_obj=False)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 241, in check_funs
    self.check_fun(testfunc, targfunc, 'arr_tdelta', **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 202, in check_fun
    testarval, targarval, targarnanval, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 160, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 88, in f
    result = alt(values, axis=axis, skipna=skipna, **kwds)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 418, in nanmax
    return _maybe_null_out(result, axis, mask)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 552, in _maybe_null_out
    if null_mask.any():
AttributeError: ("'bool' object has no attribute 'any'", 'axis: 0 of 0', 'skipna: False', 'kwargs: {}', 'testar: arr_tdelta', 'targar: arr_tdelta', 'targarnan: arr_tdelta')

======================================================================
ERROR: test_nanmean (pandas.tests.test_nanops.TestnanopsDataFrame)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 290, in test_nanmean
    allow_str=False, allow_date=False)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 213, in check_funs
    self.check_fun(testfunc, targfunc, 'arr_float', **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 202, in check_fun
    testarval, targarval, targarnanval, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 160, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 43, in _f
    return f(*args, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 88, in f
    result = alt(values, axis=axis, skipna=skipna, **kwds)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 261, in nanmean
    count = _get_counts(mask, axis)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 542, in _get_counts
    count = (mask.shape[axis] - mask.sum(axis)).astype(float)
AttributeError: ("'long' object has no attribute 'astype'", 'axis: 0 of 0', 'skipna: False', 'kwargs: {}', 'testar: arr_float', 'targar: arr_float', 'targarnan: arr_float')

======================================================================
ERROR: test_nanmin (pandas.tests.test_nanops.TestnanopsDataFrame)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 315, in test_nanmin
    allow_str=False, allow_obj=False)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 241, in check_funs
    self.check_fun(testfunc, targfunc, 'arr_tdelta', **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 202, in check_fun
    testarval, targarval, targarnanval, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 160, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 88, in f
    result = alt(values, axis=axis, skipna=skipna, **kwds)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 388, in nanmin
    return _maybe_null_out(result, axis, mask)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 552, in _maybe_null_out
    if null_mask.any():
AttributeError: ("'bool' object has no attribute 'any'", 'axis: 0 of 0', 'skipna: False', 'kwargs: {}', 'testar: arr_tdelta', 'targar: arr_tdelta', 'targarnan: arr_tdelta')

======================================================================
ERROR: test_nanskew (pandas.tests.test_nanops.TestnanopsDataFrame)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 365, in test_nanskew
    allow_complex=False, allow_str=False, allow_date=False)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 213, in check_funs
    self.check_fun(testfunc, targfunc, 'arr_float', **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 202, in check_fun
    testarval, targarval, targarnanval, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 188, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\tests\test_nanops.py", line 160, in check_fun_data
    **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 43, in _f
    return f(*args, **kwargs)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 449, in nanskew
    count = _get_counts(mask, axis)
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py", line 542, in _get_counts
    count = (mask.shape[axis] - mask.sum(axis)).astype(float)
AttributeError: ("'long' object has no attribute 'astype'", 'axis: 0 of 0', 'skipna: False', 'kwargs: {}', 'testar: arr_float', 'targar: arr_float', 'targarnan: arr_float')

----------------------------------------------------------------------
Ran 7366 tests in 516.370s

FAILED (SKIP=135, errors=5)

C:\Users\Jeff Reback\Documents\GitHub\pandas>c:\python27-64\Scripts\nosetests.exe build\lib.win-amd64-2.7\pandas\tests\test_nanops.py --pdb --pdb-failure
......C:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py:193: ComplexWarning: Casting complex values to real discards the imaginary part
  return ~np.isfinite(values.astype('float64'))
.............> c:\users\jeff reback\documents\github\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py(542)_get_counts()
-> count = (mask.shape[axis] - mask.sum(axis)).astype(float)
(Pdb) l
537         return result
538
539
540     def _get_counts(mask, axis):
541         if axis is not None:
542  ->         count = (mask.shape[axis] - mask.sum(axis)).astype(float)
543         else:
544             count = float(mask.size - mask.sum())
545
546         return count
547
(Pdb) p mask
array([False, False, False, False, False, False, False, False, False,
       False, False], dtype=bool)
(Pdb) p axis
0
(Pdb) p mask.ndim
1
(Pdb) p mask.shape[axis]-mask.sum(axis)
11L
(Pdb) p mask.sum(axis)
0
(Pdb) u
> c:\users\jeff reback\documents\github\pandas\build\lib.win-amd64-2.7\pandas\core\nanops.py(483)nankurt()
-> count = _get_counts(mask, axis)
(Pdb) l
478     def nankurt(values, axis=None, skipna=True):
479         if not isinstance(values.dtype.type, np.floating):
480             values = values.astype('f8')
481
482         mask = isnull(values)
483  ->     count = _get_counts(mask, axis)
484
485         if skipna:
486             values = values.copy()
487             np.putmask(values, mask, 0)
488
(Pdb) p values
array([-0.38825224,  2.25028687,  0.97792431,  0.05118711, -0.38908183,
       -1.25383019, -0.97858595,  0.50348946,  0.91971294,  0.18107761,
       -0.97499552])
(Pdb) p mask
array([False, False, False, False, False, False, False, False, False,
       False, False], dtype=bool)
(Pdb)
```
 The problem seems to be that the values are getting converted to a python long instead of a numpy scalar.  The workaround is easy, I can either include it in a separate patch or as part of the next one.  

But could you also try the following code and see what you get?

``` Python
a=np.zeros(11).astype('bool')
b=a.shape[0] - a.sum(0)
type(b)
```

I have tried this on linux, winpython3 x64, and pythonxy and in all of them I get `numpy.int64`.   Based on the unit test results, I would expect that you get `long` or `int`.
 At least looking at the last error, for nanskew, it doesn't appear that I have touched any of the code in that code path, so this doesn't seem to be a new bug.
 All of the errors are related to the changes for `_get_counts`

```
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\Jeff Reback>c:\python27-64\python
Python 2.7.5 (default, May 15 2013, 22:44:16) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> np.__version__
'1.8.0'
>>> a = np.zeros(11).astype('bool')
>>> b = a.shape[0]-a.sum(0)
>>> type(b)
<type 'long'>
```
 There were no changes to _get_counts.  Looking at the blame, it hasn't been touched since 2011.
 it wasn't broken before I merged your first PR.
 The first version of `test_nanops.py` didn't test 1D arrays at all, so it wouldn't have identified this problem.
 ok, its a problem now. pls have a look.
