virtual Fill:: and Outline:: methods so that Canvas::Items that cache image renderings of themselves can invalidate those caches when colors etc. change; add Item::{begin,end}_visual_change() so that we can notify the canvas more efficiently when *only* visual properties have changed and not the bounding box (probably needs to be used more widely)

libs/canvas/canvas/wave_view.h

@@ -60,6 +60,9 @@ public:
 	void set_height (Distance);
 	void set_channel (int);
 	void set_region_start (ARDOUR::frameoffset_t);
+
+        void set_fill_color (Color);
+        void set_outline_color (Color);
 	
 	void region_resized ();