sound mixer now operates on floating point, has on-the-fly resampling

sound mixer now operates on floating point, has on-the-fly resampling
(allows features like pitch shifting, and potentially doppler), and the
ogg and modplug streaming code has been largely rewritten, much cleaner
now, this saves about 4MB of ram when playing quake content at default
settings (by not resampling the wav data to 48khz anymore), snd_speed
changes will now apply to next vid_restart (tested at 48, 96, 192khz)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@11352 d7cf8633-e32d-0410-b094-e92efae38249