When reverting, we load a new image into the old image's existing
displays, and replace all references to the old image by the new image
in all GimpContext instances. We used to first update the displays and
then the contexts, which would shortly produce an inconsistent state
where the contexts were out of sync. When updating the displays with
the new image, we sometimes call menu update functions which would
then use that old image from the context when they should use the new
one, and thus triggered callbacks as if the user had activated a menu
(like image -> precision). To fix this, update the contexts before the
displays. It is also more logical to first update model objects and
then view objects.