make_SDPMedia: avoid setting port to zero

darcs-hash:20090324073047-b2873-971cde5ba034db9869ccd66432d3b2e786a2b53b
add 'chat' attribute to SCSessionNewOutgoing notification

darcs-hash:20090324073157-b2873-4f30d1baa9a3171a82bef65f1fe2ca74999ad1e0