Don't abuse/leak selection when editing velocity (fix editing velocity of a single note actually editing velocity of every note who's velocity had previously been edited).
Properly preserve selection for MIDI operations in general.
Less crap method of delineating scroll events to canvas items (no exhaustive type cases needed in editor_canvas_events.cc).
Fix silly comment style in midi_region_view.h (hans: please note this and follow in the future).
git-svn-id: svn://localhost/ardour2/branches/3.0@4343 d708f5d6-7413-0410-9779-e7cbd77b26cf
