Add cvar snd_cdautopause: optional CD track pause during game pause
Previously it was mandatory and if not desired, had to be hacked around with stuffcmd.
Also fixes:
- the CD track always being resumed when resuming from game pause, even when muted, Ref: CDAudio_SetVolume()
- bgmvolume < 0 not pausing the CD track
Edited by bones_was_here