Changed printed registration information in sip_audio_session

Ignore-this: ab7d6aeaf9e810a14695c4e6b3549830

darcs-hash:20090330121327-1e3d8-1d702874f6258813fc74e6c17d833e44eb590825
sip_session: properly unregister at the end; add --no-register option

darcs-hash:20090330124515-b2873-679270253cc5faf91760a3e04a9cfd2e4c6f96af