Group By datatype screwed when group consists of one value
x = DataFrame(np.arange(9).reshape(3,3))
x['test']=0
x['fl']= [1.3,1.5,1.6]
x.groupby('test').agg({'fl':'sum',2:'size'}).dtypes
Out[]:
2      int64
fl    object
(version 0.8)

Output in 0.7.3
Out[]:
2       int64
fl    float64

The output for x['test'] = [1,2,3] works fine
