When having emails not linked to a notification (mail.notification = False)
the link is generated without any clue about the source record.
However we can try to use model and res_id defined on the mail_mail record
to correctly format a link.
Added support of model and res_id in message_redirect_action. This method
now can redirect based on a message_id, or based on model / res_id.
bzr revid: tde@openerp.com-20131018144924-j4f22hen3lsua7cb