waveview: now that _quit is protected by a mutex, it doesn't need to be atomic

No reason to have two memory fences when we only need one

libs/waveview/waveview/wave_view_private.h

@@ -335,7 +335,7 @@ private:
 	// TODO use std::unique_ptr when possible
 	typedef std::vector<boost::shared_ptr<WaveViewDrawingThread> > WaveViewThreadList;
 
-	GATOMIC_QUAL gint _quit;
+	bool _quit;
 	WaveViewThreadList _threads;