This is a big one. Server threads talk to one another directly via
PipedOutputStreams maintained by ProdConsStructures in a mapping from
connected client InetSocketAddresses to PipedOutputStreams which are
connected to thread-side PipedInputStreams. Can now have two clients
exchange CONNECT and CONNECT_ACCEPT messages, though the CONNECT_ACCEPT
message isn't yet supported by the server, so it stops just short of a
full connection.