This patch if the first part to follow discussion on python-list
concerning problems when using distutils.config.try_run with mingw and
manifest problems on windows for python 2.6 (or any python built with
recent VS).

It simply adds strings constant got the msvcrt module, so that they can
be queried in distutils to generate manifest on the fly if needed. I
don't know which approach is best to deal with conditional compilation:
for now, I simply do not add the constants if the constants are not
defined at the C level, but this does not strike as a great idea to me.