title: Completion handler for UINavigationController "pushViewController:animated"?
body: <p>I'm about creating an app using a <code>UINavigationController</code> to present the next view controllers.
  With iOS5 there´s a new method to presenting <code>UIViewControllers</code>:</p>
  
  <pre><code>presentViewController:animated:completion:
  </code></pre>
  
  <p>Now I ask me why isn´t there a completion handler for <code>UINavigationController</code>?
  There are just </p>
  
  <pre><code>pushViewController:animated:
  </code></pre>
  
  <p>Is it possible to create my own completion handler like the new <code>presentViewController:animated:completion:</code> ?</p>