MyBB does not have a guest account by default; the forum driver was previously not assuming a virtual guest account like other forum drivers were. Added this in.

I can't remember the status of this. Were we just going to get around to test importing too before it's done?
Regardless, now I rewrote the login code, regular login and cookie login will need retesting.

I believe I was waiting on your login fix and also to test the importers. I will make sure to do that.

mybb login is not working correctly; check password authentication system