title: Codeigniter update_batch return false if no data is changed
body: <p>I have found something disturbing in codeigniter, why is when I use <code>update_batch</code> and the data to be updated is the exact same as the data in the db, it always return false.</p>
  
  <p>I can't seem to find any logical and good explanation and illustration in the CI documentation. I need it to return true even if there is no data changed, as it affect a great chunk of my codes, and only return false if failed to update db (i.e inserting a data that already exist into a unique column), then it should return false.</p>
  
  <p>One more thing, how do I show db query error message in CI ? have read that it should be <code>$this-&gt;db-&gt;_error_message()</code>, but it keeps returning <code>Call to undefined method</code>. What am I missing here ?</p>