Win32 updates.

[Ryan C. Gordon]

I've done some overhauling to the win32 code in PhysicsFS. Notable changes:

1) The DLL will now build on Visual Studio 6.0 without an updated Platform
SDK. The missing API is accessed via LoadLibrary() at runtime, so you
don't need those libraries to compile.
2) Since that missing API is dynamically loaded, we can deal with
situations where it doesn't exist on the end user's system correctly; this
means Win95/98/ME should work correctly now, too.
3) The DISABLE_NT_SUPPORT define is gone, since it isn't needed
anymore.
4) Lots of little incorrect behaviours have been corrected. (not setting
the error message in various places, etc).
5) Lots of bugs got squashed in the code audit. At least two or three
(potential) crashbugs.

Go forth and update from CVS.  :)

--ryan.