title: NSOutlineView column doesn't sort
body: <p>I can't sort a NSOutlineView in Mac OS X 10.10...</p>
  
  <pre><code>    let tableColumn = outlineView.tableColumnWithIdentifier("LocationName")
      println(tableColumn?.description)
      let sorter = NSSortDescriptor(key: "self", ascending: false)
      tableColumn!.sortDescriptorPrototype = sorter
      outlineView.reloadData()
  </code></pre>
  
  <p>neither with the code above neither setting sorting attributes in Interface Builder.</p>
  
  <p>Maybe something wrong with "self"?</p>
  
  <p>NSOutlineView column contains swift strings, compare: should work, right?
  Maybe I simply have to write a comparer?</p>