title: Rails, using the dirty or changed? flag with after_commit
body: <p>I heard rails has a dirty/change flag. Is it possible to use that in the after_commit callback?</p>
  
  <p>In my user model I have:</p>
  
  <pre><code>after_commit :push_changes
  </code></pre>
  
  <p>In <code>def push_changes</code> I would like a way to know if the name field changed. Is that possible?</p>