sip_session: remove hard coded file names for sounds

darcs-hash:20090408083800-b2873-49e563ea5cd5221a22d06c97939d38fab3c35e30
Added --trace-notifications to sip_audio_session.py

darcs-hash:20090408084059-58103-ab13f1562b557874aa9c17649b3836630bc1eeca