Avoid duplicate blocks when an account deactivates/reactivates

[jsha]

Right now if a blocked account deactivates, the next time update-blocks runs, it will notice the account is missing from /blocks/ids, will check /users/show.json, find the account is deactivated, and avoid recording an Action. However, when that account reactivates, update-blocks will record a block Action, because the diff versus the previous BlockBatch shows a new uid. This is mostly harmless, since the fanned out blocks will just be marked as duplicates, but introduces annoying and confusing redundancy in peoples' Actions lists.

This will probably be fixed by implemented AnnotatedBlocks.