zsh: Add zpython support

This adds support for building zsh with builtin python support through the zpython module. 

It is very helpful if you are running a heavy prompt like [powerline](https://github.com/Lokaltog/powerline) where shelling out to python each time the prompt gets updated causes noticeable lag.

Running powerline without zpython causes ~1sec prompt lag on my system, while with it display occurs instantly.

More info / Patch source:
http://www.zsh.org/mla/workers/2013/msg00089.html