title: NSAlert multiple buttons
body: <p>I have one NSAlert with two buttons:</p>
  
  <pre><code>var al = NSAlert()
  al.informativeText = "You earned \(finalScore) points"
  al.messageText = "Game over"
  al.showsHelp = false
  al.addButtonWithTitle("New Game")
  al.runModal()
  </code></pre>
  
  <p>It's working perfectly, but I don't know how to recognize, which button was pressed by user.</p>