Add meta_window_is_remote

It's useful for plugins to be able to easily detect whether
or not a window is from a remote host.  Also, make use of this
in the window delete codepath, instead of looking up the hostname
each time.

https://bugzilla.gnome.org/show_bug.cgi?id=620585

src/core/window.c

@@ -9115,6 +9115,21 @@ meta_window_get_client_machine (MetaWindow *window)
   return window->wm_client_machine;
 }
 
+/**
+ * meta_window_is_remote:
+ * @window: a #MetaWindow
+ *
+ * Returns: %TRUE if this window originates from a host
+ * different from the one running mutter.
+ */
+gboolean
+meta_window_is_remote (MetaWindow *window)
+{
+  g_return_val_if_fail (META_IS_WINDOW (window), FALSE);
+
+  return g_strcmp0 (window->wm_client_machine, window->display->hostname) != 0;
+}
+
 /**
  * meta_window_is_modal:
  * @window: a #MetaWindow