- There was a bug in the first implementation that would cause subsequent
  connections from a non-exempt IP address to be rejected: client_on() is
  called multiple times for a single connection - oops.
- Successfully logged in clients are now *not* counted against the concurrent
  connection limit. This way if a node hangs, the user at that IP can still
  connect/login to another node. The client has to be fully logged-in to be
  excluded from the connection count.