Later versions of windows don't allow write access to Program Files by default.

This doesn't play nicely with pycparser's desire to write lextab and yacctab files.
To work around this problem, we disable that by applying the win7_c_parser.patch
manually to C:\Python27\Lib\site-packages\pycparser\c_parser.py before running
py2exe.

Automating this is left as an exercise for some other pyweek.