Manage twisted and use new DNS lookup in sip_audio_session.py

darcs-hash:20090407121342-58103-b19b1ae58579981094092aa00700a5a23d2b512d
Only detect NAT type in sip_audio_session.py if domain has STUN servers

darcs-hash:20090407122151-58103-b6d8470475cd93a5e373f9b1c9b716679d022040