Fix signal 6 in S_Base_StartBackgroundTrack on OS X 10.9

In S_UpdateBackgroundTrack, s_backgroundLoop was passed to
S_Base_StartBackgroundTrack and tried to copy to itself using Q_strncpyz.
Move starting idlogo and intro video to cgame
Merge remote-tracking branch 'ioquake3/master'

Conflicts:
	code/client/snd_dma.c