freeze break for a11y support

[Ray Strode <halfline gmail com>]

Hi,

Matthias was doing some a11y testing and noticed that the screen
reader menu item doesn't work at the login screen:

https://bugzilla.gnome.org/show_bug.cgi?id=684474

After some yak shaving later, we were able to get it to working okay
by applying this gnome-session patch:

https://bugzilla.gnome.org/show_bug.cgi?id=663721

the patches in the original gdm bug report, and some gnome-shell patches:

https://bugzilla.gnome.org/show_bug.cgi?id=684728
https://bugzilla.gnome.org/show_bug.cgi?id=684727

Would be great if we could get this working in 3.6.0

--Ray