Layout items in the menu overwrite PopupBaseMenuItem.activate(),
so the menu stays open when selecting a layout from the menu.
Chain up to the parent class' method to make the items behave properly.
https://bugzilla.gnome.org/show_bug.cgi?id=639474
Add an indicator for the current keyboard layout, based on
libgnomekbd. The indicator is shown when more than one group
is loaded in X and it is not disabled in GSettings.
https://bugzilla.gnome.org/show_bug.cgi?id=600771