Window resizing/configuring cleanups

[Alexander Malmberg]

After my recent patch to clean up ConfigureNotify handling, a lot of
other hacks in back/Source/x11/ are unnecessary. This patch cleans
things up and optimizes the process a bit:

http://w1.423.telia.com/~u42308495/alex/window_resize_opt.patch

(Apply in core/back/.) In particular, there used to be an usleep() in
-windowdevice:, and as a result of unfortunate -back/-gui/X
interactions, -windowdevice: was being called more times than necessary,
so this might help reduce flickering (though I can't tell here; -xlib
still flickers, and always has).

Testing would be appreciated. If it doesn't cause any problems (and
especially if it seems to reduce flickering :), I'll commit it soon.

- Alexander Malmberg