title: Make Codeigniter 2.1.3 allow a Facebook backlink
body: <p>It happens that I need to fix a Codeigniter issue urgently while being in no way familiar with the tool.</p>
  
  <p>Simple question: how do I allow <strong>links back from Facebook</strong> like <a href="http://www.xxx.de/?fb_action_ids=4811819099741&amp;fb_action_types=og.likes&amp;fb_source=timeline_og&amp;action_object_map=%7B%224811819099741%22%3A447766801925104%7D&amp;action_type_map=%7B%224811819099741%22%3A%22og.likes%22%7D&amp;action_ref_map=%5B%5D" rel="nofollow">http://www.xxx.de/?fb_action_ids=4811819099741&amp;fb_action_types=og.likes&amp;fb_source=timeline_og&amp;action_object_map=%7B%224811819099741%22%3A447766801925104%7D&amp;action_type_map=%7B%224811819099741%22%3A%22og.likes%22%7D&amp;action_ref_map=%5B%5D</a></p>
  
  <p>without creating either the infamous <em>The URI you submitted has disallowed characters</em> - which I can fix by setting $config['permitted_uri_chars'] - and neither a 404 because of the internal redirects of CI.</p>
  
  <p>I'd love to learn of a quick fix for that issue.</p>