title: MagicalRecord does not save new objects
body: <p>I setup my MagicalRecord stack like so:</p>
  
  <pre><code>MagicalRecord.setupAutoMigratingCoreDataStack()
  let moc = NSManagedObjectContext.MR_defaultContext()
  moc.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
  </code></pre>
  
  <p>Now when I create and want to save my object, I get <code>success</code> of <code>false</code> but the returned <code>error</code> is <code>nil</code> too. Also the object still has a <code>temporaryID</code> set to <code>true</code>.</p>
  
  <pre><code>let product =  Product.MR_createEntity()!
  
  MagicalRecord.saveWithBlock({ (ctx) -&gt; Void in
      product.timeStamp = NSDate()
      product.title = "Some title"
  }) { (success, error) -&gt; Void in
  
      if !success{
          // No success but error is nil
  
      }
  }
  </code></pre>