Mutegroups and Same Note Retrigger

Hi Ken,
A bug indeed, too enthousiastic housekeeping 
Replace line 53 in modules/audio.py:
            if e.sound.stopmode==3 or e.sound.stopmode==-1:    # keep track of backtrack/once status
            if e.sound.stopmode==3:    # keep track of backtrack status

Other options:

• wait till next release: I'm preparing it and will include this fix.
  
• use the fixed key trickery noek proposed, inspiring for other use too
  

Regards, Hans