Removed spurious global statement from sip_audio_session.py

darcs-hash:20081212152135-58103-fbb4a993258a2dc09c75cdcaa62e96aceb984691
Ported multi-transport, new route lookup and SIP URI parsing functions, and SIP trace file logging to sip_message.py

darcs-hash:20081212152310-58103-05afd3109382e18037e724dc058a94d206118e6a