Re-Integrate

Reverse all the things.

Figured out that I've been approaching this problem entirely in the wrong direction:

- Since Boxen only ships what's in the Cellar then the canonical `site-packages` should be IN the Cellar. `/opt/boxen/homebrew/lib/python2.7/site-packages` is now a symlink.
- Pip and Distribute are once again installed with the Python package to prevent them from creating their own `site-packages` directory.