[trunk] setting beam properties mostly doesn't react to undo.

Add four 1/16 notes.
- Drag "Beam start" onto the 3rd note. Works. Undo. Nothing happens.
- Drag "Beam start" onto the 3rd note. Works. Drag "Beam middle" onto 3rd note. Works. Undo. Nothing happens.
- Drag "No Beam" onto any note. Works. Undo. Works.
- Drag "32nd beam sub" into the 3rd note. Works. Undo. Nothing happens.

But undo seems to do something. Try this:
While all four notes are connected by a double beam, drag "Start beam" onto the 3rd note.
Works, you now have two groups of two. Undo. Nothing happens.
Now drag "No beam" onto the 3rd note. Effect: 3rd and 4th note now have no beam but a hook. Undo.
Aha, it goes back to four connected notes, as if the first undo had done something.

R5367.