pydata/pandas — pull request #3483 by jreback (2013-04-29 16:06:30+00:00)
Title: BUG: GH3468 Fix assigning a new index to a duplicate index in a DataFrame would fail

partially fixes #3468

This would previously raise
````
In [6]: df = DataFrame([[1,2]], columns=['a','a'])

In [7]: df.columns = ['a','a.1']

In [8]: df
Out[8]:
a a.1
0 1 2

```