Code review comment for lp:~stefanor/ibid/factoid-330901

I don't like the AuthExceptions. We already have a mechanism for handling auth
failures which works fine with factoids. Modify stuff seems fine, although I
had an issue with a pattern matching multiple values even though it should
only match one. The SQLAlchemy stuff in factoids is still a bit dodgy... :-/
 review needs_fixing