Message 80858 - Python tracker

In bug 4804, there is some debate about how desirable it is for Python
to unconditionally disable all CRT assertions on Windows - however,
there is agreement that exposing the ability to enable and disable these
assertions via the msvcrt module is reasonable - so I'm attaching a
patch for exactly that.  I'd also like to nominate this for the 2.6 and
py3k branches.