In addition to checking the current settings, check also if the
zoom region is active before registering the event listener.
This way, we avoid DBus traffic for events we're not interested in.
Also, make FocusCaretTracker resilient to multiple register/deregister
calls (which can now happen).
https://bugzilla.gnome.org/show_bug.cgi?id=724305
Have AT-SPI calls time out after 250ms, to mitigate the effect of a
deadlock when querying another application that is trying to query
gnome-shell.
https://bugzilla.gnome.org/show_bug.cgi?id=708387
A11y users who use the magnifier may have trouble
focusing when they're typing or trying to keynav.
Implement a new system so that they can have the
magnifier track the caret and focus instead instead
of just the mouse.
Bug https://bugzilla.gnome.org/show_bug.cgi?id=647074
