user preference system

[slingamn]

This is a follow-up to #458. We should have a general system for account flags, in particular:

1. Opting in to the bouncer behavior
2. Opting in to znc.in/self-message even for clients that don't know how to request it

NS ENFORCE should maybe get folded into this system (leaving ENFORCE as an alias for compatibility)

[DanielOaks]

Makes sense to introduce this, definitely.

[slingamn]

We should have a similar user preference for announcing new session attaches to fellow channel participants (the equivalent of a JOIN line).

[slingamn]

We should have one for enabling/disabling HistServ messages for JOIN and PART (we're turning this off by default in #474).

[slingamn]

You should be able to opt into autoreplay-on-join (even control the number of lines you get, up to a limit).

[slingamn]

You should be able to opt into a variant of autoreplay-on-join that, upon reattach, plays all the messages it thinks you missed.

Basically, this is an alternative to RESUME: you transparently reattach to your client and it tries to catch you up. (It'll work better with clients that can deduplicate by msgid.)

[slingamn]

jwheare notes that "all relevant clients" can handle self-messages. I'm leaning towards sending them all the time, no opt-out pref (if nobody needs it then it's just clutter), and even stripping out the znc.in/self-message cap.

[slingamn]

Update: advertise the cap, but ignore its value.

[slingamn]

Fixed in #499