Manual merge with wilmer's approach to handling missing protocols
Turns out he already implemented pretty much the same thing in the
parson branch... last year.
The differences between the two approaches are subtle (there aren't too
many ways to do this, some lines are the exact same thing) but I decided
I like his version better, so this mostly reverts a handful of my
changes while keeping others. The main advantage of his approach is that
no fake protocols are registered, no actual prpl functions are called,
and the missing prpl is a singleton constant.
New things compared to the implementation in the other branch:
- The explain_unknown_protocol() function.
- Fixed named chatrooms throwing a warning and losing the "account"
setting when saving. See changes in irc_im.c
- Fixed the "server" setting dropping when saving. See account.c
Differences with my previous implementation:
- Accounts with missing protocols don't autoconnect
- 'account list' marks them as "(missing!)"
