revert (and update) mistakenly removed line from 082d12b
revert most of 16f5f91

I mistakenly thought SDL_MaoRGB returned a pixel value even for palettized surfaces
SDLSprite: dont indiscriminately set RLE
SDLSprite: we only ever want RLE for colorkey/alpha blits

no need to have a method for this just set it when we set colorkey/alpha
comment out sprite conversion since we dont currently fully support 16bpp