Disable RANDR's fake Xinerama protocol when there's more than one screen.

... in the protocol sense.  Xinerama doesn't have any provision for more
than one protocol screen each with its own geometry.

Red Hat bug #231257.

randr/rrxinerama.c

@@ -428,6 +428,14 @@ RRXineramaExtensionInit(void)
 	return;
 #endif
 
+    /*
+     * Xinerama isn't capable enough to have multiple protocol screens each
+     * with their own output geometry.  So if there's more than one protocol
+     * screen, just don't even try.
+     */
+    if (screenInfo.numScreens > 1)
+	return;
+
     (void) AddExtension(PANORAMIX_PROTOCOL_NAME, 0,0,
 			ProcRRXineramaDispatch,
 			SProcRRXineramaDispatch,