sip_session: print the filename where MSRP tracing goes

darcs-hash:20090407103500-b2873-231b477501d438ec54f353bd7bb60a4ae729bfe4
Manage twisted and use new DNS lookup in sip_message.py

darcs-hash:20090407105821-58103-523fc290a2e38199a1c917621ee5719f2ffda243