* Create a request within a dialog keeping non system header from an initial request. This function is very usefull to resend request after expiration or chalange.
* Create a request within a dialog keeping non system header from an initial request. This function is very useful to resend request after expiration or chalenge.
* @param obj dialog associated to the request
* @param initial_req, all headers + body are re-used from this request except: Via,From, To, Allows, CSeq, Call-ID, Max-Forwards