title: How to implement a UINavigationController for modal presentation, not for popover, with an adaptive segue
body: <p>While using a universal storyboard and adaptive segues, how can one implement a Present As Popover segue that will have a navigation bar (with a title and close button) only on iPhone when presented modally, and will not have a navigation controller on iPad when presented as a popover?</p>
  
  <p>I believe the proper setup is to not include a nav controller in the storyboard, control-drag to the new view controller and select a Present As Popover segue. Then in <code>prepareForSegue</code> one will need to create the navigation controller and embed the destination controller in it, then add the title and buttons, but only if it will be presented modally. If that approach is correct, how can one do that in code?</p>