title: Changing the UIBackButtonItem title
body: <p>I have a navigationController-based app. I want to change the title of the back button for the root view controller. I have tried the following code in the rootViewController's viewDidLoad method, but no success:</p>
  
  <pre><code>self.navigationItem.backBarButtonItem.title = @"Back";
  </code></pre>
  
  <p>Any ideas?</p>