BUG: pandas 0.13 Series argmax/argmin returns index label instead of location (changed from 0.12)
------------------------ pandas 0.12 --------
In [14]: pd.**version**
Out[14]: '0.12.0'

In [15]: a=pd.Series(range(3), index=('2','3','4'))

In [16]: a.argmax()
Out[16]: 2

In [17]: a.idxmax()
Out[17]: '4'

------------------------ pandas 0.13 --------
In [2]: pd.**version**
Out[2]: '0.13.0'

In [3]: a=pd.Series(range(3), index=('2','3','4'))

In [4]: a.argmax()
Out[4]: '4'

In [5]: a.idxmax()
Out[5]: '4'
