Travis, python 3.4 and caching
So python 3.4 beta1 is out, and eventually travis will roll out 3.4 support. 
Out test matrix is already bulky and partial at the same time.

I see travis [introduced](http://about.travis-ci.org/docs/user/caching/) a caching mechanism into their infrastructure. Previous attempts to do the same thing
using a network cache brought build times down to [2-3 minutes](https://travis-ci.org/y-p/pandas/builds/6422326) for most builds (i.e. those with no no cython changes). 
We could squeeze in more test matrix coverage that way, while almost certainly making the CI more brittle.

Thoughts?
