Undo is also confused with narrow-to-region

[Oliver Kiddle <okiddle@xxxxxxxxxxx>]

Within narrow-to-region, undo will put back the full BUFFER that is then
duplicated from PREDISPLAY/POSTDISPLAY. After narrow-to-region, the
opposite problem occurs with the part that was not part of the BUFFER
being lost.

This isn't that easy to solve. recursive-edit could save and restore the
undo structures but for some uses of recursive-edit, such as that shown
for it in the manual, that might not be the right thing anyway.

Oliver