allow `--user` with homebrew Python

by patching distutils instead of setting install.prefix in distutils.cfg

This follows the pattern used by various System Pythons
(OS X, Debian) where sys.prefix is not the default install prefix.

The patch is based on the diff between Python.org 2.7 and OS X 10.9 System Python 2.7.
python: update 2.7.8 bottle.
python3: update 3.4.1 bottle.