title: Setting back button when presenting a view controller
body: <p>On clicking a button I display a view controller using the following code:</p>
  
  <pre><code>let navController = UINavigationController(rootViewController: locationVC)
  navController.navigationBar.barTintColor = StyleHelper.navBarColor()
  navController.navigationBar.tintColor = UIColor.whiteColor()               
  navController.navigationItem.backBarButtonItem = UIBarButtonItem(image: UIImage(named: "back_arrow"), style: .Plain, target: locationVC, action: nil)
  self.presentViewController(navController, animated: true, completion: nil)
  </code></pre>
  
  <p>But the back button does not appear on the locationVC</p>
  
  <p>What am I doing wrong? Please help</p>