Require explicit types when removing PlayHandles in the Mixer

This fixes a few deadlocks where a PresetPreviewPlayHandle would be removed by
the creation of a new PresetPreviewPlayHandle.

include/Mixer.h

@@ -224,7 +224,7 @@ public:
 		return m_playHandles;
 	}
 
-	void removePlayHandles( Track * _track, bool removeIPHs = true );
+	void removePlayHandlesOfTypes( Track * _track, const quint8 types );
 
 	bool hasNotePlayHandles();
 

include/PlayHandle.h

@@ -40,11 +40,10 @@ class PlayHandle : public ThreadableJob
 public:
 	enum Types
 	{
-		TypeNotePlayHandle,
-		TypeInstrumentPlayHandle,
-		TypeSamplePlayHandle,
-		TypePresetPreviewHandle,
-		TypeCount
+		TypeNotePlayHandle = 0x01,
+		TypeInstrumentPlayHandle = 0x02,
+		TypeSamplePlayHandle = 0x04,
+		TypePresetPreviewHandle = 0x08
 	} ;
 	typedef Types Type;