msvc build

Hi,
I got the latest from github and I'm having some problems with the build using the free version of vc9. I believe there have been some recent improvements with the cygwin build which have conflicted with the msvc one.

First IoSystem.c had setenv is commented out. This is necessary with msvc since it doesn't have such a call. While we're at it can we agree that msvc code is denoted by using the WIN32 define, and cygwin is __CYGWIN__. In a couple of places this is getting confused with _WIN32. Currently the msvc build defines WIN32 on the command line.

Also the makefiles have recently changed to call libraries foo.lib instead of libfoo.lib, fine but AddonBuilder.io doesn't know this and spits out "missing library" messages.

I'll be pushing fixes to these to my github repo, any comments?

- James