What to do with irow in case of duplicate index?
Since irow translates the integer index to a label one and then retrieves the row, in case of duplicate index multiple rows are returned.

``` python
In [34]: df = pandas.DataFrame(np.random.rand(3,3), columns=list('ABC'), index=list('aab'))

In [35]: df
Out[35]:
          A         B         C
a  0.031057  0.528825  0.694592
a  0.705572  0.122005  0.754107
b  0.475423  0.048636  0.224495

In [36]: df.irow(0)
Out[36]:
          A         B         C
a  0.031057  0.528825  0.694592
a  0.705572  0.122005  0.754107

In [37]: df.irow(1)
Out[37]:
          A         B         C
a  0.031057  0.528825  0.694592
a  0.705572  0.122005  0.754107

In [38]: df.irow(2)
Out[38]:
A    0.475423
B    0.048636
C    0.224495
Name: b

```
