Fix focus handling with multiple awesome instances

When there are multiple X11 screens (i.e. :0.0 and :0.1) for zaphod mode
style X setups, this triggers a refresh of focus when the instance
running on a particular root receives the mouse

Fixes https://github.com/awesomeWM/awesome/issues/599.

event.c

@@ -580,6 +580,12 @@ event_handle_enternotify(xcb_enter_notify_event_t *ev)
         }
         lua_pop(L, 1);
     }
+    else if (ev->event == globalconf.screen->root) {
+        /* When there are multiple X screens with awesome running separate
+         * instances, reset focus.
+         */
+        globalconf.focus.need_update = true;
+    }
 }
 
 /** The focus in event handler.