Changed setup.py to work no matter where it is called from. We were previously

using __file__, which isn't consistent on Windows. Some awesome debugging (and
patch) here from Karen Tracey. Fixed #6562.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7139 bcc190cf-cafb-0310-a4f2-bffc1f526a37