if SDL is built with a non-cdecl calling convention, and it's just generally
bad practice anyhow.
Now programs explicitly call SDL_Quit() where appropriate, wrap SDL_Quit() in
a cdecl function where it can't be avoided, and rely on the parachute where
a crash might have hit the atexit() before (these ARE test programs, after
all!).
From: "Mike Gorchak"
added help and options -mono to force monochrome RGB2YUB conversion and
-lum <percent> - luminance of image during conversion. Also rewritten code
which moves overlay into window. Now it depends on window size.
Also fully rewritten -scale option, image now scaling from 50% from center
of screen until border of window is reached - it really tests scaler, old
-scale test doesn't test downscale.
