Catch SystemError thrown in 3.6
Trying to set an attribute on a non-empty timeseries now on 3.6
causes an SystemError here, which it didn't used to, which breaks
things.

In [28]: s = pandas.Series()

In [29]: s.test = 'test'

In [30]: s = pandas.Series([0] * 100, pandas.to_datetime(list(range(100)), unit='s'))

In [31]: s
Out[31]:
1970-01-01 00:00:00    0
1970-01-01 00:00:01    0
1970-01-01 00:00:02    0
1970-01-01 00:00:03    0
1970-01-01 00:00:04    0
1970-01-01 00:00:05    0
1970-01-01 00:00:06    0
1970-01-01 00:00:07    0
1970-01-01 00:00:08    0
1970-01-01 00:00:09    0
1970-01-01 00:00:10    0
1970-01-01 00:00:11    0
1970-01-01 00:00:12    0
1970-01-01 00:00:13    0
1970-01-01 00:00:14    0
1970-01-01 00:00:15    0
1970-01-01 00:00:16    0
1970-01-01 00:00:17    0
1970-01-01 00:00:18    0
1970-01-01 00:00:19    0
1970-01-01 00:00:20    0
1970-01-01 00:00:21    0
1970-01-01 00:00:22    0
1970-01-01 00:00:23    0
1970-01-01 00:00:24    0
1970-01-01 00:00:25    0
1970-01-01 00:00:26    0
1970-01-01 00:00:27    0
1970-01-01 00:00:28    0
1970-01-01 00:00:29    0
                      ..
1970-01-01 00:01:10    0
1970-01-01 00:01:11    0
1970-01-01 00:01:12    0
1970-01-01 00:01:13    0
1970-01-01 00:01:14    0
1970-01-01 00:01:15    0
1970-01-01 00:01:16    0
1970-01-01 00:01:17    0
1970-01-01 00:01:18    0
1970-01-01 00:01:19    0
1970-01-01 00:01:20    0
1970-01-01 00:01:21    0
1970-01-01 00:01:22    0
1970-01-01 00:01:23    0
1970-01-01 00:01:24    0
1970-01-01 00:01:25    0
1970-01-01 00:01:26    0
1970-01-01 00:01:27    0
1970-01-01 00:01:28    0
1970-01-01 00:01:29    0
1970-01-01 00:01:30    0
1970-01-01 00:01:31    0
1970-01-01 00:01:32    0
1970-01-01 00:01:33    0
1970-01-01 00:01:34    0
1970-01-01 00:01:35    0
1970-01-01 00:01:36    0
1970-01-01 00:01:37    0
1970-01-01 00:01:38    0
1970-01-01 00:01:39    0
dtype: int64

In [32]: s.test = 'test'
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
pandas/index.pyx in pandas.index.DatetimeEngine.get_loc (pandas/index.c:11572)()

pandas/hashtable.pyx in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:6931)()

TypeError: an integer is required

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
pandas/indexes/base.py in get_loc(self, key, method, tolerance)
   1944             try:
-> 1945                 return self._engine.get_loc(key)
   1946             except KeyError:

pandas/index.pyx in pandas.index.DatetimeEngine.get_loc (pandas/index.c:11740)()

pandas/index.pyx in pandas.index.DatetimeEngine.get_loc (pandas/index.c:11646)()

pandas/index.pyx in pandas.index.DatetimeEngine._date_check_type (pandas/index.c:11810)()

KeyError: 'test'

During handling of the above exception, another exception occurred:

TypeError                                 Traceback (most recent call last)
pandas/index.pyx in pandas.index.DatetimeEngine.get_loc (pandas/index.c:11572)()

pandas/hashtable.pyx in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:6931)()

TypeError: an integer is required

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
pandas/tseries/index.py in get_loc(self, key, method, tolerance)
   1430         try:
-> 1431             return Index.get_loc(self, key, method, tolerance)
   1432         except (KeyError, ValueError, TypeError):

pandas/indexes/base.py in get_loc(self, key, method, tolerance)
   1946             except KeyError:
-> 1947                 return self._engine.get_loc(self._maybe_cast_indexer(key))
   1948

pandas/index.pyx in pandas.index.DatetimeEngine.get_loc (pandas/index.c:11740)()

pandas/index.pyx in pandas.index.DatetimeEngine.get_loc (pandas/index.c:11646)()

pandas/index.pyx in pandas.index.DatetimeEngine._date_check_type (pandas/index.c:11810)()

KeyError: 'test'

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
ValueError: Error parsing datetime string "test" at position 0

The above exception was the direct cause of the following exception:

SystemError                               Traceback (most recent call last)
<ipython-input-32-753b248023e5> in <module>()
----> 1 s.test = 'test'

pandas/core/generic.py in __setattr__(self, name, value)
   2695         else:
   2696             try:
-> 2697                 existing = getattr(self, name)
   2698                 if isinstance(existing, Index):
   2699                     object.__setattr__(self, name, value)

pandas/core/generic.py in __getattr__(self, name)
   2668             return object.__getattribute__(self, name)
   2669         else:
-> 2670             if name in self._info_axis:
   2671                 return self[name]
   2672             return object.__getattribute__(self, name)

pandas/tseries/base.py in __contains__(self, key)
    182     def __contains__(self, key):
    183         try:
--> 184             res = self.get_loc(key)
    185             return lib.isscalar(res) or type(res) == slice or np.any(res)
    186         except (KeyError, TypeError, ValueError):

/dpandas/tseries/index.py in get_loc(self, key, method, tolerance)
   1437
   1438             try:
-> 1439                 stamp = Timestamp(key, tz=self.tz)
   1440                 return Index.get_loc(self, stamp, method, tolerance)
   1441             except (KeyError, ValueError):

pandas/tslib.pyx in pandas.tslib.Timestamp.__new__ (pandas/tslib.c:9668)()

pandas/tslib.pyx in pandas.tslib.convert_to_tsobject (pandas/tslib.c:26065)()

pandas/tslib.pyx in pandas.tslib.convert_str_to_tsobject (pandas/tslib.c:27849)()

pandas/src/datetime.pxd in datetime._string_to_dts (pandas/tslib.c:92986)()

SystemError: <class 'str'> returned a result with an error set

 - [ ] closes #xxxx
 - [ ] tests added / passed
 - [ ] passes ``git diff upstream/master | flake8 --diff``
 - [ ] whatsnew entry

needs tests # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15399?src=pr&el=h1) Report
> Merging [#15399](https://codecov.io/gh/pandas-dev/pandas/pull/15399?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ff0deecbc8f8e9ae3d274e5e7cd7c0056de1a6c2?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.


```diff
@@           Coverage Diff           @@
##           master   #15399   +/-   ##
=======================================
  Coverage   90.42%   90.42%           
=======================================
  Files         134      134           
  Lines       49377    49377           
=======================================
  Hits        44650    44650           
  Misses       4727     4727
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15399?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/tseries/index.py](https://codecov.io/gh/pandas-dev/pandas/compare/ff0deecbc8f8e9ae3d274e5e7cd7c0056de1a6c2...3f3bd5bef714706ad7ef64af1443b3b161c9da26?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvaW5kZXgucHk=) | `95.42% <100%> (ø)` | :white_check_mark: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15399?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15399?src=pr&el=footer). Last update [ff0deec...3f3bd5b](https://codecov.io/gh/pandas-dev/pandas/compare/ff0deecbc8f8e9ae3d274e5e7cd7c0056de1a6c2...3f3bd5bef714706ad7ef64af1443b3b161c9da26?el=footer&src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). looks ok to me. but you can certainly add this as a test if you'd like.

```
(py3.6) bash-3.2$ ipython
Python 3.6.0 |Continuum Analytics, Inc.| (default, Dec 23 2016, 13:19:00) 
Type "copyright", "credits" or "license" for more information.

IPython 5.1.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: pd.__version__
Out[1]: '0.19.0+452.gff0deec'

In [2]: s = pandas.Series([0] * 100, pandas.to_datetime(list(range(100)), unit='s'))

In [3]: s.head()
Out[3]: 
1970-01-01 00:00:00    0
1970-01-01 00:00:01    0
1970-01-01 00:00:02    0
1970-01-01 00:00:03    0
1970-01-01 00:00:04    0
dtype: int64

In [4]: s.test = 'test'

``` pls create a new issue if you'd like to add a test.