Rewrote MidiEvent to be a well-behaved self-contained object that optionally owns it's buffer, has proper copying semantics, etc.
Fixed crazy bugs triggered by adding lots of events with varying times to a region.
Speed up initial session display significantly (don't redraw each MIDI region tons of times, though still happens more than once and can use fixing...).
git-svn-id: svn://localhost/ardour2/trunk@2213 d708f5d6-7413-0410-9779-e7cbd77b26cf
d7db3f757f