present: Disable when Xinerama is active

Among much else Present depends on RANDR types, and RANDR isn't properly
Xinerama-aware yet anyway.

Reviewed-by: Julien Cristau <jcristau@debian.org>
Signed-off-by: Adam Jackson <ajax@redhat.com>

present/present_screen.c

@@ -206,6 +206,11 @@ present_extension_init(void)
     ExtensionEntry *extension;
     int i;
 
+#ifdef PANORAMIX
+    if (!noPanoramiXExtension)
+        return;
+#endif
+
     extension = AddExtension(PRESENT_NAME, PresentNumberEvents, PresentNumberErrors,
                              proc_present_dispatch, sproc_present_dispatch,
                              NULL, StandardMinorOpcode);