title: NSConcreteNotification is received, but not defined?
body: <p>I'm writing preferences for my app which registers it for launch at login (using <code>LSSharedItemList</code> API). All goes fine and my app toggles its presence in user's login items upon checkbox status. Now I want to tackle another problem when user actually removes the app from "Login items" in <code>Accounts.prefPane</code>.</p>
  
  <p>Using Notification Watcher I see that distributed notification center sends <code>com.apple.loginItemsListDidChnage</code> (mind the typo) notification, hence I add observer for that notification with same selector (which is <code>IBAction</code>) that handles checkbox in preferences window (which, actually, [un]registers the app from/to login items).</p>
  
  <p>The problem appears when I try to compare the class of the sender of the action that toggles my app as login item. Using <code>[sender description]</code> and <code>[sender class]</code> I see <code>NSConcreteNotification</code> class, but as soon as I try to do comparison upon it - code breaks saying that there is no such class defined:</p>
  
  <pre><code>if ([[sender class] isEqualTo:[NSConcreteNotification class]]) {
    ...
  }
  </code></pre>
  
  <p>If I try to compare sender to <code>NSNotification</code> - then flow doesn't fall into that branch.</p>
  
  <p>Maybe I'm missing some essential knowledge on distributed notifications in Mac OS X?</p>
  
  <p>Running Mac OS X 10.6.2</p>