title: Swift protocols: method does not override any method from its superclass
body: <p>Since Xcode 6 still has a lots of bugs with Swift, I'm not sure is it one or I'm missing something.
  My class adopts protocol NSLayoutManagerDelegate. But it seems impossible to override method I need. I do as documentation describes:</p>
  
  <pre><code>override func layoutManager(_ aLayoutManager: NSLayoutManager!,
          didCompleteLayoutForTextContainer aTextContainer: NSTextContainer!,
          atEnd flag: Bool) {
  
      }
  </code></pre>
  
  <p>But I get error here: method does not override any method from its superclass.
  What should I do?</p>