* Ensure that going from one to the other tears down the former and
its plugins before instantiating the latter and its plugins.
UIManager: Unify Event sending & broadcasting
* Make the two behave the same way (walk the widget stack from top to
bottom), and properly handle the window stack shrinking shrinking
*and* growing.
Previously, broadcasting happened bottom-to-top and didn't really
handle the list shrinking/growing, while sending only handled the list
shrinking by a single element, and hopefully that element being the one
the event was just sent to.
These two items combined allowed us to optimize suboptimal
refresh behavior with Menu and other Menu classes when
opening/closing a document.
e.g., the "opening document" Notification is now properly regional,
and the "open last doc" option no longer flashes like a crazy person
anymore.
Plugins: Allow optimizing Menu refresh with custom menus, too.
Requires moving Menu's close_callback *after* onMenuSelect, which, eh,
probably makes sense, and is probably harmless in the grand scheme of
things.
Simplify (and avoid edge cases) in other code by having
ReadHistory manage the "lastfile" setting on add, remove,
rename...
Fixed a few other cases of things not updated.
