title: Programmatically changing the identifier property of UIBarButtonItem
body: <p>Through Interface Builder I have the ability to change the Identifier of a UIBarButtonItem to something like "Add" (or "Undo", "Redo" etc...). This gives my button a nice "+" image.</p>
  
  <p>How can I set this programatically? The UIBarButtonItem does not accept a "setIdentifier" message.</p>