Change the "overlay" actor to be a group of 4 actors that we can
rearrange so as to have a hole in the middle (to cover up the whole
screen except for the highlighted icon). For non-iconified windows, we
still highlight them the old way (raising them above the overlay),
because we don't want square highlights around shaped windows.
Make the indicator in the pop-up move faster.
Quickly fade in the "overlay" window when starting, rather than
showing it abruptly. Destroy it right away rather than just hiding it
when the AltTabHandler is destroyed.
Fix the font size to be the same as the "Activities" button.
Fix a warning when tabbing past an iconified window.
This is a fairly simple implementation, not all that different from
plain metacity's. Further improvements could be made to
js/ui/altTab.js in the future.
http://bugzilla.gnome.org/show_bug.cgi?id=580917
