DataFrame.groupby.fillna for axis=1, no filling happens
groupby.fillna not working along column axis.

The bug exists for 15.1 and 15.2
Works for 13.1

```
import pandas as pd
import numpy as np

print pd.__version__

test = pd.DataFrame(index=pd.MultiIndex.from_product([['value1','value2'],pd.date_range('2014-01-01','2014-01-06')]),
                    columns=pd.Index(['1','2'], name='id'))
test['1'] = [np.nan, 1, np.nan, np.nan, 11, np.nan, np.nan, 2, np.nan, np.nan, 22, np.nan]
test['2'] = [np.nan, 3, np.nan, np.nan, 33, np.nan, np.nan, 4, np.nan, np.nan, 44, np.nan]
testT = test.T

print '*' * 30
print test
print '*' * 30
print test.groupby(level=0, axis=0).fillna(method='ffill')
print '*' * 30
print testT
print '*' * 30
print testT.groupby(level=0, axis=1).fillna(method='ffill')
print '*' * 30
```
