SDL helper libs prerelease

I’m gearing up to release new versions of the SDL helper libraries
that I maintain:
SDL_image, SDL_mixer, SDL_net, and SDL_ttf

The projects have been updated to build on all platforms supported
by the SDL library. I have built them on: Windows, MacOS Classic,
MacOS X, mingw32 cross-compile, and Linux.

Please try out these prerelease versions and let me know if there are
any problems as soon as possible.

-Sam Lantinga, Software Engineer, Blizzard Entertainment