[sdlsound] alt audio converter

[Ryan C. Gordon]

> Also, I can't help but getting nervous about things like
>
>    buffer[i] = ((int) *(src++) + *(src++) ) >> 1;

I'm not sure what the actual C spec says about this (probably "undefined
behaviour"), but in practical terms, I have seen CodeWarrior "miscompile"
similiar constructs.

> Despite these complaints, let me emphasise that I am pleased and excited
> about the prospect of new and improved conversion filters. They just need a
> few more bugfixes, that's all. :-)

You fixes are in CVS, thanks!

--ryan.