use shutdown() method of MSRPTransport instead of loseConnection

darcs-hash:20090209141359-b2873-a3987e5f9c0808a52e6544b698b5b3dc52c8097e
minor fix

darcs-hash:20090209141440-b2873-e9d3963dcbbb849aee914d337f6c889d812008e2