Add a gtk_shell.set_startup_id request, so the application can communicate
to the compositor the startup id that it received through the
DESKTOP_STARTUP_ID envvar, or other means.
https://bugzilla.gnome.org/show_bug.cgi?id=762268
Add set_modal ond unset_modal to the gtk_surface interface. When a
surface is modal, the compositor can treat it differently from non-modal
dialogs, for example attach it to the parent window if any. There is
currently no changes to input device focus; it is up to the client to
ignore events to the parent surface that is wanted.
This bumps the gtk_shell version to 2.
https://bugzilla.gnome.org/show_bug.cgi?id=745720