title: Determining when a UIPageViewController scrolls past last page
body: <p>I'm attempting to dismiss a UIPageViewController which is presented modally when the user scrolls past the last page. Is there a way to tell when this happens? 
  viewControllerAfterViewController is called when the last view controller is shown.</p>
  
  <p>Edit: I've also tried to add UISwipeGestureRecognizers but they are not being called.  I think this is because the UIPageViewController's gesture recognizer's disable them.</p>