message: Replaced view controller if crumbs equal
  It only comes in here when replacing the current view and changing State. Replacing the current controller means the pop animation runs
diff: [_navigationController setViewControllers:allControllers animated:true];
  }
  }
  + if (crumb == currentCrumb) {
  + NVSceneView *scene = (NVSceneView *) [_scenes objectAtIndex:crumb];
  + if (!![scene superview])
  + return;
  + NVSceneController *controller = [[NVSceneController alloc] initWithScene:scene];
  + NSMutableArray *controllers = [NSMutableArray arrayWithArray:_navigationController.viewControllers];
  + [controllers replaceObjectAtIndex:crumb withObject:controller];
  + [_navigationController setViewControllers:controllers animated:true];
  + }
  }
  - (void)notifyForBoundsChange:(NVSceneController *)controller
  