title: UIPageViewController: pageViewController:spineLocationForInterfaceOrientation: not called
body: <p>my spineLocationForInterfaceOrientation-method is not called; therefore, the spine is always on the left, but I would like to have it in the middle... what am I doing wrong?</p>
  
  <pre><code>if ([UIPageViewController class]) {
      self.pageViewController = [[UIPageViewController alloc]
          initWithTransitionStyle:UIPageViewControllerTransitionStylePageCurl
          navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
      self.pageViewController.view.backgroundColor = [UIColor redColor];
      self.pageViewController.delegate = self;
  
      NotesPageController *notesPageController = [[NotesPageController alloc]
          initWithNibName:@"NotesPageController" bundle:nil];
      NSArray *pageViewControllers = [NSArray arrayWithObjects:notesPageController, nil];
      [self.pageViewController setViewControllers:pageViewControllers
          direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:NULL];
  
      self.pageViewController.dataSource = self;
  
      [self addChildViewController:self.pageViewController];
  
      [self.navigationController pushViewController:self.pageViewController animated:NO];
  }
  </code></pre>
  
  <p>Thanks a lot!</p>