minor fix for misleading comment
some deep tweaking to get MIDI channel control into nearly done shape for 3.1
major fixes for MIDI patch change and note undo/redo. Patch change handling was completely broken because of the use of absolute floating point comparisons for time comparison, and serialization/deserialization of patch change property changes was borked because of int/char conversions by stringstream. Note undo/redo would fail for note removal if a note had been moved and/or had its note number changed as the next operation after it was added, because time-based lookup would fail. Similar small changes made for sysex messages, which just needed the musical_time comparisons and nothing else
Merge branch 'master' of git.ardour.org:ardour/ardour