Read sip_transports config option in sip_audio_session.py

darcs-hash:20081209134253-58103-89a7e9a3a53b0687eda3e837c10530ec0117c3f0
Added docstring and comments to RFC 3263 lookup function

darcs-hash:20081209145816-58103-c842f9656cf7e655a8b9088283d62c32b7f05f2e