title: Problems with migration from one CoreData model to another
body: <p>I created new version of CoreData model (added one new attribute to entity) and mapping from one to another. Then I open document created with old model. It opens normally but when I tried to save it I get alert window with "<strong>The document “Blahblahblah” could not be saved as “Blahblahblah.blah”. An error occurred while saving.</strong>" and message in debug console</p>
  
  <pre><code>AppKit called rmdir("/private/var/folders/v9/y2tl4yh55zj1pcg0typksyrm0000gp/T/TemporaryItems/(A Document Being Saved By Document 3)"), it didn't return 0, and errno was set to 66.
  </code></pre>
  
  <p>Have you got ideas what is it meen?</p>
  
  <p>PS. It is not my first experience in CoreData migration but it's first time I stuck so hard.</p>