renamed do_trace_pjsip to trace_pjsip

darcs-hash:20081107094421-b2873-238728f4c9912fb35901ca4e1f4d3acbf831c01b
made InvitationBuffer a proxy, so it can be attached to existing object

darcs-hash:20081107094643-b2873-6b6b367ba0a2aecdba56cbfe8e0ac731e04927a9