Windows version in the windows builds

[Rod Widdowson]

Mostly for Scott,

All our project files for the windows build tie _WIN32_WINNT to be 0x0400 .  This was the tag for NT V4 (the one before Windows
2000).

I'm not proposing making any changes to this in the VC2010 builds.

I'd like to move this on the VC2014 builds (which I'll move to be VC2017 builds "soon") to be 0x600.  This is the tag for
Vista/W2K8.  This should make no difference at all since the VC2014 builds won't support XP (or earlier) because of another
completely different setting you need to make.

This will require a small amount of fleet-footedness in the code I am currently writing, but I can live with that.

Rod