* fixed corruption bugs due to allocation hell of MidiModel::const_iterator::_event: Changed it into boost::shared_ptr
* fixed MidiModel::const_iterator bugs:
-First note on lost, if an automation event comes first
-corrupt MidiEvent compared to automation event if there are no notes in the region
* (hopefully) fixed possible race condition
* fixed range check in MidiDiskstream::set_state for channel mask
* treating notes with duration 0 more gently in MidiRegionView (warning instead of assertion)
git-svn-id: svn://localhost/ardour2/branches/3.0@3345 d708f5d6-7413-0410-9779-e7cbd77b26cf