Fix SMFSource to realloc a scratch read buffer as necessary, removing upper limit on single raw event size. Remove public exposure of MidiBuffer::max_event_size (though it still exists internally). Fix crash bug on MIDI record completion (transport stop). git-svn-id: svn://localhost/ardour2/trunk@2157 d708f5d6-7413-0410-9779-e7cbd77b26cf