* libxfce4menu/xfce-menu-item.{c,h}: Add support for the Comment field

	  via xfce_menu_item_get_comment().
	* libxfce4menu/xfce-menu-monitor.{c,h}: Add support for defining what
	  kind of files/directories are monitored (XfceMenuMonitorFlags,
	  xfce_menu_monitor_set_flags(), xfce_menu_monitor_get_flags(),
	  xfce_menu_monitor_has_flags()).
	* libxfce4menu/xfce-menu.c: Check monitor flags before adding
	  files/directories to the monitoring system.
	* tests/test-display-menu.c: Center window on screen.

git-svn-id: https://svn.xfce.org/svn/xfce/libxfce4menu/trunk@26527 a0aa69c2-05f4-0310-b83c-d5d913b14636