title: setRightBarButtonItems doesn't work
body: <p>I am trying to have 2 buttons on the right of a <code>UINavigationBar</code>. Below is the source code. No error but there is no button either. It is a <code>UIViewController</code>, not a <code>UINavigationViewController</code></p>
  
  <pre><code>let buttonEdit: UIButton = UIButton.buttonWithType(UIButtonType.Custom) as! UIButton
  buttonEdit.frame = CGRectMake(0, 0, 40, 40)
  buttonEdit.setImage(UIImage(named:"me44.png"), forState: UIControlState.Normal)
  buttonEdit.addTarget(self, action: "rightNavItemEditClick:", forControlEvents: UIControlEvents.TouchUpInside)
  var rightBarButtonItemEdit: UIBarButtonItem = UIBarButtonItem(customView: buttonEdit)
  
  let buttonDelete: UIButton = UIButton.buttonWithType(UIButtonType.Custom) as! UIButton
  buttonDelete.frame = CGRectMake(0, 0, 40, 40)
  buttonDelete.setImage(UIImage(named:"me44.png"), forState: UIControlState.Normal)
  buttonDelete.addTarget(self, action: "rightNavItemDeleteClick:", forControlEvents: UIControlEvents.TouchUpInside)
  
  var rightBarButtonItemDelete: UIBarButtonItem = UIBarButtonItem(customView: buttonDelete)
  
  // add multiple right bar button items       
  self.navigationController?.navigationItem.setRightBarButtonItems([rightBarButtonItemDelete, rightBarButtonItemEdit] as [AnyObject], animated: true)
  
  //I also tried code below no luck either
  self.navigationItem.setRightBarButtonItems([rightBarButtonItemDelete, rightBarButtonItemEdit] as [AnyObject], animated: true)
  </code></pre>