locking. removed simsound. removed unused S_AmbientOff() and S_AmbientOn(). other
multiple cleanups and fixes.
snd_sdl.c: replaced the old broken implementation which used to cause LRU failures
with the one adapted from the uhexen2 project.
sound.h: added missing prototypes, including the new SNDDMA_LockBuffer().
git-svn-id: http://svn.code.sf.net/p/quakespasm/code/trunk/quakespasm@6 af15c1b1-3010-417e-b628-4374ebc0bcbd