can't retry sign up if previous email unconfirmed

[roadscape]

To reproduce:

1. Go through signup, do not confirm email
2. Restart signup, use same email; nothing happens when you click 'Continue'

It appears to override 'username' field of the existing pending entry; not sure this is wise. Faucet should allow multiple unverified records to exist with the same email. Uniqueness should only be enforced among verified emails.

This behavior seems to be accompanied by Unhandled rejection Error: Can't set headers after they are sent. in the logs, which might explain why nothing happens (no visual feedback anyway) when one clicks 'Continue' in the 2nd step.