title: UISplitViewController: how to go back from Detail to Master
body: <p>I am using a <code>UISplitViewController</code> to implement a Master/Detail flow app.</p>
  
  <p>I am not using a Navigation Controller.</p>
  
  <p>To go from the <strong>MasterViewController</strong> to the <strong>DetailViewController</strong> I am using:
  <code>performSegueWithIdentifier("showDetail", sender: self)</code></p>
  
  <p>What should I use to go back from the <strong>DetailViewController</strong> to the <strong>MasterViewController</strong>?</p>