irc: Update IRC code to use simpler suspendable ports system.

irc: Update IRC code to use simpler suspendable ports system.

* 8sync/systems/irc.scm (irc-socket-setup): Set port to be non-blocking.
  (install-socket, make-basic-irc-handler): Remove.
  (irc-loop): New procedure; uses the Guile read-line code to switch
  from the former manual-buffering of make-basic-irc-handler to simply
  using Guile's read-line utility.
  (queue-and-start-irc-agenda!): Use irc-loop.