Expected connection and disconnection

[DanielOaks]

Scripts assume that clients:

1. Connect at the start of the script.
2. Never disconnect.

This is a bad assumption if we're going to be testing messages like QUIT, features like MONITOR and WATCH, and other sorts of things.

To do this, add a new client definition marker (!? or something, maybe?) that marks the given client will be connected in the future. Also mark a way to connect and disconnect clients. Maybe > to connect 'em, < to disconnect 'em, and <? to say 'process incoming messages until the client disconnects'.

[DanielOaks]

Adding the <? marker first, that's a good one to have for testing a command like QUIT.

[DanielOaks]

The <? marker is now added. I had to change the actual command line to accept name:< LINE HERE as well because for something like QUIT the PING we run afterwards to sync it fails, so it'd never get to the separate <? line. Example script added which goes through it all good.