title: Codeigniter Cart: Adding an item to cart more than once replaces
body: <p>Using CI 2.1.1 and the native Cart library</p>
  
  <p>If I insert an item (with same product id, same options) more than once, it replaces instead of increasing the qty.</p>
  
  <p>Could this be a bug, am I missing something, or what would be the best way to add this functionality myself?        </p>