iterrows turns some columns from int64 to float64
``` python
>>> import pandas as pd
>>> pd.version.version
'0.15.2'
>>> df = pd.DataFrame({u'A': {123.0: 2.0}, u'B': {123.0: 1}})
>>> df
     A  B
123  2  1
>>> df['B'].dtype
dtype('int64')
>>> type(df.iterrows().next()[1]['B'])
<type 'numpy.float64'>
```
