title: Call onunload function from iframe
body: <p>I am working on a multiplayer chess game as a Facebook app.
  If one player leaves the game by closing the browser the other player should get a notification. So if one player closes the Browser, a unlink function should be called to unlink the player. This works fine with <code>onunload</code> outside Facebook.
  The problem is, that the Facebook apps are loaded in iframes and the <code>onunload</code> event doesn't work there.</p>
  <p>So I need a way to call a function inside an iframe when a user is closing the browser.</p>