title: Can't customize pushViewController's back button
body: <p>I've got a ViewController which opens up another ViewController by</p>
  
  <pre><code>[self.navigationController pushViewController:detailViewController animated:YES];
  </code></pre>
  
  <p>Now the new VC has got a back button in the navBar but I can't manage to give it the same background image as the navBar buttons from the first ViewController. I've tried with:</p>
  
  <pre><code>UIImage *buttonImage = [UIImage imageNamed: @"Button.png"];
  [self.navigationItem.backBarButtonItem setBackButtonBackgroundImage:buttonImage forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
  [self.navigationItem.backBarButtonItem setTitle:@"doesnt work either"];
  </code></pre>
  
  <p>But it doesn't work. What am I doing wrong? Thank you!</p>