Remove systray icons from the save set

This commits makes awesome remove systray windows from the save set when they
are unmapped. This happens for the same reason as with normal client windows.

Signed-off-by: Uli Schlachter <psychon@znc.in>

event.c

@@ -704,6 +704,7 @@ event_handle_unmapnotify(void *data __attribute__ ((unused)),
             {
                 xembed_window_array_take(&globalconf.embedded, i);
                 widget_invalidate_bytype(widget_systray);
+                xcb_change_save_set(globalconf.connection, XCB_SET_MODE_DELETE, ev->window);
             }
 
     return 0;