title: Need to return to the presenting UIViewController from within a presented UINavigationController
body: <p>In MyMainViewController, I present a navigation controller like this:</p>
  
  <pre><code>UIStoryboard* storyboard = [UIStoryboard storyboardWithName:@"Main_iPhone" bundle:nil];
  UINavigationController* nc = [storyboard instantiateViewControllerWithIdentifier:@"NAVIGATION_CONTROLLER_ID"];
  [self presentViewController:nc animated:YES completion:nil];
  </code></pre>
  
  <p>Later, from somewhere within the view hierarchy of the UINavigationController, I need to return to MyMainViewController. How can I do this?</p>
  
  <p>(Note: MyMainViewController is defined in a .XIB, and not in the storyboard where the UINavigationController and it's children are defined.)</p>