Made further refinements to the audioengine:

-Looping syncslaves are stopped when there is no syncmaster.
-Hardened against edge cases regarding soundsource priority sorting.
-Fixed issue with syncmasters being marked as having looped when instead they just started playing (caused double-start of syncslaves).
-Updated some comments.

indra/llaudio/llaudioengine_fmodex.cpp

@@ -810,6 +810,7 @@ void LLAudioChannelFMODEX::cleanup()
 	Check_FMOD_Error(mChannelp->stop(),"FMOD::Channel::stop");
 
 	mChannelp = NULL;
+	mLastSamplePos = 0;
 }