/startTestdrive_action
action to test-drive this layout in the current session.

Sourcecode in Layout/actions.js:
1:   function startTestdrive_action() {
2:      session.data.layout = this;
3:      if (req.data.http_referer)
4:         res.redirect(req.data.http_referer);
5:      else
6:         res.redirect(res.handlers.context.href());
7:      return;
8:   }