Don't assume Registration_state with state == "unregistered" always includes a code in scripts

darcs-hash:20090108141750-58103-83a13ebeca6372a2eb46fa4e5b8f81772790fad9
Better description for the SIP protocol

darcs-hash:20090108155829-58252-234cb47ceab36f20b91f51050044e514b440b4f4