BUG/API: assignment of frame in a multi-indexed column frame with a matching level
http://stackoverflow.com/questions/24553921/pandas-matching-on-level-of-hierarchical-index/24554350#24554350

This should align on the columns axis. Not clear how to specify the alignment level though (e.g. broadcasting would be tricky here).

```
import numpy as np
import pandas as pd

arrays = [np.hstack([ ['one']*3, ['two']*3]), ['Dog', 'Bird', 'Cat']*2]
columns = pd.MultiIndex.from_arrays(arrays, names=['foo', 'bar'])

df = pd.DataFrame(np.zeros((3,6)),columns=columns,
                  index=pd.date_range('20000103',periods=3))

df['one'] = pd.DataFrame({'Bird' : np.ones(3)*2,
                          'Dog' : np.ones(3),
                          'Cat' : np.ones(3)*3},
                          index= pd.date_range('20000103',periods=3))
df['two'] = pd.DataFrame({'Dog' : np.ones(3)*4,
                          'Bird' : np.ones(3)*5,
                          'Cat' : np.ones(3)*6,},
                          index= pd.date_range('20000103',periods=3))
```
