[metacity] ui: set x11 as only allowed backend

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 9254a4eb79278a6fd56d428f52a4a6a5755fc28f
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Mon Feb 22 14:45:37 2016 +0200

    ui: set x11 as only allowed backend
    
    https://bugzilla.gnome.org/show_bug.cgi?id=762445

 src/ui/ui.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/ui/ui.c b/src/ui/ui.c
index cffb1f6..ef22a4b 100644
--- a/src/ui/ui.c
+++ b/src/ui/ui.c
@@ -63,6 +63,8 @@ meta_ui_init (int *argc, char ***argv)
   gdk_disable_multidevice ();
 #endif
 
+  gdk_set_allowed_backends ("x11");
+
   if (!gtk_init_check (argc, argv))
     meta_fatal ("Unable to open X display %s\n", XDisplayName (NULL));
 }