Unexpected behavior on Series.irow (Series.iget) with non-unique index
Hi,

`Series.irow(i)` (and also `Series.iget(i)`), with `i` being an integer, returns more than one value on Series with non-unique indexes if the index at location `i` has duplicates. This is not the behavior I expected and it is also different from the behavior shown by `DataFrame.irow(i)`, since it only returns the row located at position `i` regardless of any existing index duplicates. Also the documentation for `Series.irow`/`Series.iget` specifies that an "int" parameter should return a "scalar" value, so I guess this might be a bug.

Here is some sample code I've run using pandas '0.8.2.dev-f5a74d4':

```
In [52]: s = Series([0, 1, 2], index=[0, 1, 0])

In [53]: s.irow(0)  # here I was expecting 0
Out[53]: 
0    0
0    2

In [54]: s.irow(1)
Out[54]: 1

In [55]: s.irow(2)  # here I was expecting 2
Out[55]: 
0    0
0    2

```

and its DataFrame counterpart:

```
In [56]: df = DataFrame([[0], [1], [2]], index=[0, 1, 0])

In [57]: df.irow(0)
Out[57]: 
0    0
Name: 0

In [58]: df.irow(1)
Out[58]: 
0    1
Name: 1

In [59]: df.irow(2)
Out[59]: 
0    2
Name: 0
```

Thanks and regards.
