DataFrame.groupby.count sometimes returns Series instead of DataFrame
In version 0.11.0

``` python
A = DataFrame([[1,1],[2,1]],columns=['X','Y']).groupby('X').count()
```

returns a DataFrame, when there are 2+ grouping levels...

but,

``` python
B = DataFrame([[1,1],[1,1]],columns=['X','Y']).groupby('X').count()
```

returns a Series, when there is only 1 grouping level. 

In version 0.10.0, B would also be a DataFrame. 

Don't know if this was by design, but it seems awkward to check the type before using B downstream. 
