[pycrypto] _fastmath.c now compiles with VC++ 2008

[Thorsten Behrens]

Dwayne,

I've committed a couple changes to git.

The changes allow _fastmath.c to compile using VC++ 2008 Express.

The changes to setup.py allow the use of libmpir as an alternative to 
libgmp. The main reason for that latter change is that mpir, which is a 
gmp fork, is friendly to being built with VC++, whereas gmp is not. As 
libmpir comes with a gmp.h header, only setup.py needed to be changed 
for libmpir support.

Let me know if I'm not using your source repository in the way you 
intended it, btw.

All the best
Thorsten