title: Avoid post update event if domain was not updated or was not dirty
body: <p>We had registered post update event listener for all the domain classes. But its being called every time we save an existing record even if any fields of that domain class was not updated.</p>
  
  <p>For example:</p>
  
  <pre><code>User userInstance = User.get(1)
  userInstance.save()
  </code></pre>
  
  <p>That post update event listener get called for the above code where <code>userInstance</code> was not dirty. How can we avoid this?</p>
  
  <p>Using grails 2.3.5 with mongo 3.0.1 with no hibernate installed.</p>