title: Custom NSViewController representedObject doesn't update when view selection changes
body: <p>I've got a custom NSViewController that's also an NSOutlineViewDataSource. I also have a window with an NSOutlineView bound to an instance of my view controller as the data source, and the NSOutlineView bound to the view: property of the custom view controller.</p>
  
  <p>The controller fills the outline view fine. However, selections within the view don't automatically update the representedObject property of the controller. The only thing that seems to trigger a change in representedObject is when I call setRepresentedObject: directly... which sort of defeats the purpose.</p>
  
  <p>Any idea why that might be? representedObject <em>is</em> supposed to update automatically, right? Thanks in advance...</p>