Update to python 2.7.8

This is a verbatim copy of homebrew's python formula, without the old
scripts_directory change for pip/distutils, and is **experimental**
Remove homebrew revision from formula

We use `-boxen*` suffixes for the same result, and the revision
causes our bo-janked binary handling to break
Remove the python env script

It's no longer necessary, as homebrew's python is configured to install
scripts to $HOMEBREW_ROOT/bin
Have to fill in content
Merge pull request #28 from boxen/python-2.7.8

Python 2.7.8
More options

* Add support for different python interpreters to mkvirtualenv (aka pypy
  support)
* Add name overrides to pip to install the same package in multiple virtualenvs
Change workon to source

Depending on virtualenvwrapper is not so good in this module. There's still
some assumptions about it being used, but this at least removes some of the
ways of virtualenvwrapper can cause this to fail (all the hook scripts for
example)
Fix usage of env.sh