[IronPython] Use of msvcr100 in msvcrt module

[Jeff Hardy]

In the 2.7 msvcrt module, msvcr100 is currently used as the p/invoke
target (which is the VS2010 version of the MS Visual C Runtime). Was
this chosen on purpose? I fear that it msvcrt100 probably isn't
present on most systems (without installing the redistributable),
while plain ol' msvcrt probably is.

The problem is that, officially speaking, msvcrt.dll is part of the OS
and not to be used by third-party software. In reality, I don't think
it's an issue, as it's unlikely that basic C functions are going to
change any time soon.

So, do we toe the party line and put up with the redistribution
hassle, or do we make the distribution easier but risk possible (but
unlikely) breakage in the future?

- Jeff