PEP: pandas/core round 5 (nanops, ops, panel*)
Looks good, but:

```
$ flake8 pandas/core/nanops.py 
pandas/core/nanops.py:401:41: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:491:16: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:491:42: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:492:16: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:492:42: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:499:45: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:528:16: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:528:42: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:529:16: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:529:42: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:530:17: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:530:43: E226 missing whitespace around arithmetic operator
pandas/core/nanops.py:545:33: E226 missing whitespace around arithmetic operator

$ flake8 pandas/core/ops.py 
pandas/core/ops.py:94:41: E226 missing whitespace around arithmetic operator
```
 Well this is fun:

```
(development)roch@roch ~/Software/pandas $ flake8 pandas/core/nanops.py
(development)roch@roch ~/Software/pandas $ flake8 pandas/core/ops.py
(development)roch@roch ~/Software/pandas $ git status
On branch pep8-round5
Untracked files:
  (use "git add <file>..." to include in what will be committed)

    pandas/version.py

nothing added to commit but untracked files present (use "git add" to track)
(development)roch@roch ~/Software/pandas $ 
```
 that's pretty old file. how did that slip in?
 I was just doing that to show no local changes.  Seems in pep8 version 1.6 they no longer enforce whitespace around the operator. I'm using 1.6.2.
 @rockg that's super fun! for the preservation of our sanity let's settle on the >= 1.6 behavior; `**` isn't all that common anyhow
 thank you!
