Simplify the logic of duplication of NoteTrack. Duplicates are always in
serialized state. Un-serialization can happen on demand in any of the
NoteTrack operations that require a defined sequence.
Changing the duration of the sequence after paste is needed,
as it was also needed, when I fixed Stretch at commit
90eb4ec142f7d575d0870dd9c755589bff520cbe. I don't know if this should be
considered a bug in Allegro that we are compensating.
* Fix memory leaks.
* Add comments about initializations and checking for successful results.
* Add checks for NULL deref.
* Consistency in "TODO" vs "TO-DO" comments!
