v2: a small tweak to leave a tidier footprint for git-blame.


Also, some slight corrections on the timeline:


  Jan 20, 2003 - Register autojoin function with `erc-after-connect'
                 hook, which passes in `erc-announced-server-name' for
                 function's server param

  Jun 26, 2005 - Add dialed server as fallback when announced name
                 missing

  Sep 16, 2005 - Deprecate `erc-announced-server-name' in favor of
                 `erc-server-announced-name'

  Jan 05, 2017 - Switch from announced to dialed, ignoring server param
                 provided by `erc-after-connect' hook

  Sep 16, 2021 - Switch from dialed to announced, but consider networks

    This patch - Stay the course, but always fall back to dialed (not
                 just when unset)

    Bug #48598 - Prefer unique session identifiers based around and
                 compatible with networks, but fall back on announced,
                 then dialed (for compatibility)