BUG: astype assignment with loc not working

[TomAugspurger]

In [10]: df = pd.DataFrame({'A': [1., 2., 3., 4.]})

In [11]: df.dtypes
Out[11]: 
A    float64
dtype: object

In [12]: df.loc[:, 'A'] = df['A'].astype(np.int64)

In [13]: df.dtypes
Out[13]: 
A    float64
dtype: object

#4624 (which closed #4312) fixed it for .iloc

[jreback]

@TomAugspurger thanks for the report...was a tad tricky, because normally I don't coerce a float block at all (it can get expensive if you have to nan check it), but only needs coercing if you are exactly replaceing the values (all of them)