rem: conn->outputheaders = newheaders;
add: conn->outputheaders = Ns_SetCopy(newheaders);
context: Ns_ConnReplaceHeaders(Ns_Conn *conn, Ns_Set *newheaders){    newheaders = Ns_SetCopy(newheaders);    Ns_SetFree(conn->outputheaders);    conn->outputheaders = newheaders;}