Code review comment for lp:~bzr/bzr/transport_post_connect_hook

Have addressed the smart transport case by moving the hook callback down into the medium classes where the connection actually happens. The one wrinkle here is that the medium then gets passes rather than transport. I think this is preferable to having the medium and transport hold references to each other, and the medium classes also have a disconnect method. This should make the hook useful, without actually needing to restructure the transport classes quite yet.