title: Override UINavigationController's UINavigationTransitionView clipToBounds
body: <p>I am creating a custom segue to do custom animation (page curl) when pushing/popping a UINavigationController. The animation works fine except for the fact that it's clipped to the boundaries of the UINavigationController. I've checked all the related views to make sure <code>clipToBounds</code> are set to <code>NO</code>, no luck.</p>
  
  <p>Then I looked at the view hierarchy of UINavigationController itself and found the culprit, a subview of type UINavigationTransitionView. Setting this view's clipToBound to NO does the trick. However, since the view is most likely private and undocumented, it feels hacky/brittle. Is there any other way to accomplish this?</p>