[sdlsound] New Core Audio backend decoder

[Ryan C. Gordon]

> My repo can be found at:
> http://hg.assembla.com/SDL_sound_CoreAudio

This looks pretty good; I'll pull from your repo soon and play around 
with it.

Killing quicktime.c was on my TODO list...is there any reason to keep it 
in light of the CoreAudio decoder?

--ryan.