email_for_token now returns whether the user must set a password to finish...

email_for_token now returns whether the user must set a password to finish adding an email to their browserid account.  also write (failing) tests for imminent changes to complete_email_addition api.  also refactor db layer, adding haveVerificationToken to move code off of emailForVerificationToken that only cares about whether a verification token exists or not.  whew.