/stopTestdrive_action
stop a layout test and resume normal browsing.

Sourcecode in Layout/actions.js:
1:   function stopTestdrive_action() {
2:      session.data.layout = null;
3:      res.message = new Message("layoutStopTestdrive");
4:      if (req.data.http_referer)
5:         res.redirect(req.data.http_referer);
6:      else
7:         res.redirect(res.handlers.context.href());
8:      return;
9:   }