MSRPChat: use create a logger if trace_msrp is set

darcs-hash:20090324114019-b2873-1b9600ecc190cfe3eb9ffba56a4b64ea23884b11
Allow application to set Contact URI for Invitation and Subscription

darcs-hash:20090324114651-58103-2b3839ba81ef4c298c8f97a7cc4efc701ec2f6c9