Also:
- fix issues where the Undo action in the Browse screen was not
consistent with the main window. The existing hook signature has been
changed; from a snapshot of the add-on code from a few months ago, it
was not a hook that was being used by anyone.
- change the undo shortcut in the Browse window to match the main
window. It was different because undoing a change in the editing area
could accidentally trigger an undo of an operation, but the damage is
limited now that (most) operations can be redone. If it still proves to
be a problem, perhaps we should just always swallow ctrl+z when an
editing field is focused.
