title: How to change Back button text from within the child view controller?
body: <p>I know that you can set the title of the back button from the IB or in <code>prepareForSegue</code>, but in my app I need to update the title according to events that can happen while the controller is visible.</p>
  
  <p>I tried but nothing happens:</p>
  
  <p><code>self.navigationItem.backBarButtonItem = UIBarButtonItem(title: title, style: .Plain, target: nil, action: nil)</code></p>
  
  <p>This works though but has no back arrow:</p>
  
  <p><code>self.navigationItem.leftBarButtonItem = UIBarButtonItem(title: title, style: .Plain, target: nil, action: "popVC")</code></p>
  
  <p>Any ideas?</p>