title: Change back button title when pushing a UIViewController on UITableViewController
body: <p>View hierarchy:</p>
  
  <pre><code>UINavigationController
        -&gt;UITableViewController(1)
               -&gt;UITableViewController(2)
                     -&gt;UIViewController(3)  
  </code></pre>
  
  <p>In 1 and 2 I have this code:</p>
  
  <pre><code>override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
      self.navigationItem.backBarButtonItem?.title = ""
  }
  </code></pre>
  
  <p>It should override the back button title of the next view controller pushed on the current view controller. It works from 1 -> 2. But it does not work for 2 -> 3. In 3 the back button title has a title, the name of the previous UITableViewController.</p>
  
  <p>Any ideas whats wrong? I am using swift, xcode6.1 and iOS8.1</p>