The hot-spots for resizing a window by dragging its corner are now
limited to a small area around the actual corner instead of an area with
1/3rd the length or width of the window.
The hot-spots to resize a window while holding a modifier key and the
right mouse button are unchanged.
Refactors restore helper into move_to_front_and_make_active().
Fixes not bringing all modal children to the front when any modal
child or its modeless parent is clicked.
