title: Getting last saved object id
body: <p>I am using the Model_CRUD class and it's methods to save and find in database. 
  The problem comes when saving new object into DB, is how to get last inserted id ?</p>
  
  <pre><code>User::forge($userInfo)-&gt;save(); // Save returns only bool value
  </code></pre>
  
  <p>Does this requires one query more to get last inserted id ?</p>