tighten up elsewhere failure page

Fixes #2978.
Well, we have to populate the local db somehow. For the test I decided to populate the local db the way it will have been populated in production: by hitting the `/on/twitter/Gratipay/` page before ever the failure page is hit. That's what I mean by "primed" at https://github.com/gratipay/gratipay.com/pull/2982/files#r21307192.