[SDL] sdl sound

[Ryan C. Gordon]

> I worked at improving the support for 4/6 channels off and on this
> summer, but I've given it up now, since no one seems to be interested.

I wouldn't say "no one is interested" ... it's definitely something that
_should_ get supported sooner or later.

I _am_ concerned about the legacy code that will break when the
assumptions about 1 vs. 2 channels are no longer accurate, but oh well.

The Mythical SDL 1.3 should really support > 2 channel out of the box,
if you ask me.

--ryan.