title: .ajaxPrefilter() jQuery
body: <p>I would like to filter all ajax response. I found this jQuery function: jQuery.ajaxPrefilter().
  Can someone tell me how this works?
  When the users didn't logged on then I must catch that php response ( fe.: "not_logged_on" ) because the time when it must do as in normal case.</p>
  
  <p>for example:</p>
  
  <pre><code>jQuery.ajaxPrefilter(function( response ){
     if ( response == 'not_logged_on' )
         window.location = "?login";
  })
  </code></pre>
  
  <p>I hope understandable my question.</p>