nanmin no longer works with series
Using NumPy's nanmin on a pandas Series worked as expected, now however the Series is returned with each element set to the minimum, rather than just getting the minimum. Not sure if this is a Numpy of Pandas issue.

```
np.nanmin(pds.Series([1,2,3,4]))
Out[14]: 
0    1
1    1
2    1
3    1
dtype: int64

np.min(pds.Series([1,2,3,4]))
Out[15]: 1
```
