Pandas 0.18.1 groupby and resample with multilevel aggregation error
Initially posted here: http://stackoverflow.com/questions/38861244/pandas-0-18-1-groupby-and-resample-with-multilevel-aggregation-error

From the documentation at the below links, both df3_resample and df4_resample should return the same dataframe, however df4_resample throws an exception. 

http://pandas.pydata.org/pandas-docs/version/0.18.0/whatsnew.html#whatsnew-0180-breaking-resample

http://pandas.pydata.org/pandas-docs/version/0.18.1/whatsnew.html#groupby-syntax-with-window-and-resample-operations

```
df = pd.DataFrame(np.random.rand(10,4),
                  columns=list('ABCD'),
                  index=pd.date_range('2010-01-01 09:00:00', periods=10, freq='s'))
df['item'] = 'item_a' # add column for groupby

df3_resample = df.groupby('item').apply(lambda x: x.resample('2s').agg({'A': {'A_mean': np.mean, 'A_max': np.max}}))

df4_resample = df.groupby('item').resample('2s').agg({'A': {'A_mean': np.mean, 'A_max': np.max}})
```
