fix re-drawing of splitting icon
rework metering states 2, 6, 18 and 22
possible fix for http://tracker.ardour.org/view.php?id=5586
meter-state 17 and 49 + code-comment
bump actual publically visible version (oops)
work around sparse motion notification events when tooltips are disabled

fixes http://tracker.ardour.org/view.php?id=5174