rationale pathways that add notes to Sequence<T> so that there is only final insertio...

rationale pathways that add notes to Sequence<T> so that there is only final insertion step; when changing note properties that affect "indexing" within a Sequence<T> (i.e. via set<T,comparator> indexing/ordering/hashing), remove the note and add it back so that indexing stays consistent; fix marshalling of MidiModel::DiffCommand (boost::bind(&Object::method, reference_to_object) will COPY the reference, so use a pointer); fix MidiModel::find_note() to compare note properties not pointer addresses

git-svn-id: http://subversion.ardour.org/svn/ardour2/ardour2/branches/3.0@7203 d708f5d6-7413-0410-9779-e7cbd77b26cf