Eliminate a double-copy on MIDI playback (MidiRingBuffer -> MidiBuffer). Various MIDI diskstream/source/SMF fixes (only write when appropriate, handle transport locates, etc). Fix MIDI rec region size/offset problems. Code cleanups. git-svn-id: svn://localhost/ardour2/trunk@1934 d708f5d6-7413-0410-9779-e7cbd77b26cf