Forcibly disable DNS lookups from within PJSIP to prevent blocking

darcs-hash:20090303155711-58103-94fb44a12a3c6e15111014688282c9225b5420dd
Use received transport endpoint as Contact URI in incoming Invitation instead of Request URI

darcs-hash:20090303163810-58103-2b0fe0d422d143756022048ac1d9c94a5228e633