servers should attempt to open connections to clients

[zooko]

Currently each client attempts to open a connection to each server. If it were the case that a server were behind NAT or firewall and connections couldn't be opened to that server, but that server were able to open connections out to clients, then if it did so the clients would be able to use that connection to issue requests to the server.

To do this, servers should ask the introducer(s) to tell them about all clients and then servers should attempt to establish a foolscap connection to each client. If there is already such a connection (because, for example the client has already opened a connection to the server) then foolscap will automatically deduplicate and keep just one working connection.