make Hit (percussive note display item) actually draw something and fix up its coordinates
use CANVAS_DEBUG_NAME instead of explicit #ifdef to set canvas item name
comment edit
trivial API change for MidiRegionView::update_hit()
tweak Polygon::render() to work whether or not fill or outline are unset
fix apparent logic error for MidiRegionView when redisplaying note model
fix missing Hit destructor, which left polygons all over the canvas after deleting the Hit object(s)