This is necessary since the default "waveout" driver on windows is
incompatible to Quake II (due to too big output buffers) and "dsound"
can't be forced since it's not available on some installations. The
default driver is choosen by platform:
Windows -> dsound
FreeBSD -> dsp
Linux -> alsa
Copied and adapted (hopefully) all relevant code from Q2Pro.
Did some small refactorings when needed.
Still TODO:
* Adapt Makefile
* OGG support when using OpenAL
* A cvar that switches between OpenAL and DMA/SDL
* Actually compiling and testing this stuff ;)