EnsurePerson fails for new maintainers during upload processing

If a correctly-signed package is uploaded with a typo in the maintainer email address (or more generally, a maintainer email for which we do not have an account) it fails rather than being rejected during parseAddress() with:

http://launchpadlibrarian.net/35140507/mWrWmk0XCcF5NXAUQL3ouAhHpTl.txt

InternalError: Slony-I: Table account is replicated and cannot be modified on a subscriber node

Looks very related to the new account setup.

As a side note, for the case of a typo in the maintainer field, it'd be great if instead of assuming that the maintainer is someone other than the uploader/signer, we checked the distance between the two addresses? (although, people *could* in theory use a slightly different email address intentionally in the maintainer field - such as <email address hidden>).