Fix cache key collision and add test for cache key distinctness.
Fixes #7420.

tests ok in windows?
 I ran tests for python 3.4.

I can run tests for earlier versions tomorrow if you like.

On 16 June 2014 22:01, jreback notifications@github.com wrote:

> tests ok in windows?
> 
> —
> Reply to this email directly or view it on GitHub
> https://github.com/pydata/pandas/pull/7478#issuecomment-46236814.
 this looks good....all tests green on windows now!

thanks!
 Fantastic, at last! Thanks very much for your help.
 no thank you!
