Cleanup and cross platform work for python building-utility. (Tested on Python2.7 and Python3.3)

Saw that acidia was trying to make this code cross platform and decided to help. It no longer uses windows method of separating directories in file paths, instead using the cross platform magic that python has.

There are also some bug fixes and refactoring. It now requires Python 2.5 or greater.

This is my first pull request, please ask questions and let me know if I need to change anything.