Making gnome-screensaver auto-lock in XFCE

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http://askubuntu.com – gnome-screensaver has been vastly simplified for major version 3 and no longer supplies the preferences dialog. It is now only useful for locking the screen and providing an unlock dialog. I use 12.04 LTS at the moment and am able to install gnome-screensaver version 3.4.1-0ubuntu1 and add it to the XFCE session's application autostart list. gnome-screensaver then works when I select Lock Screen from the panel. I am, however, unable to configure gnome-screensaver to auto-lock the screen. There is no obvious configuration file or dialog where I can set the timeout. Right now I use xscreensav (HowTos)