pandas.rolling_* functions lose the name of the input Series
``` python
In [10]: s = pd.Series(np.arange(1000.0), name='foo')

In [11]: s.name
Out[11]: 'foo'

In [12]: pd.rolling_mean(s, 30).name is None
Out[12]: True

In [13]: pd.__version__
Out[13]: '0.16.2'
```
