title: How to change the backButtonItem title on a UIViewController?
body: <p>I feel daft asking this question, but I haven't been able to get this to work. I have a NavController->TableViewController->WebViewController. I'm trying to change the title of the backButton on the WVC from the default "Back" to "Reference".</p>
  
  <p>This should be a simple matter of setting the text property of the Back button either in Storyboard (which isn't working) or in code of my WebViewController's viewDidLoad method: </p>
  
  <pre><code>    self.navigationItem.backBarButtonItem.title = @"Reference";
  </code></pre>
  
  <p>Is this just a bug or am I missing something? </p>