Add support for away-notify capability

Add support for away-notify capability

Add support for away-notify. As nicks change status, update ircuser
objects with new away status and messages, no /whois needed.

Modify automatic WHO polling when away-notify is active to poll all
channels ONCE regardless of polling settings and nick-limit.  This
captures away state for existing nicks in the channel.  Channels
joined after this will queue a separate one-off WHO poll.

Queue one-time WHO of nicks who join a channel when away-notify is
active as some servers won't send an :away message in this situation.
To support this, autoWhoQueue can now check specific users.

See http://ircv3.net/specs/extensions/away-notify-3.1.html