Fix #263 "cannot manually add repo that was swapped before"
Pretends that the swap repo never existed, by deleting it before adding
the new repo, and showing the same message that is shown when a new
repo is added. This does not change behaviour for existing non-swap
repos. They are not deleted before being added again, or else we would
lose the ability to verify the fingerprint of an existing repo is the
same as a newly added one with the same URL.
Note that this has the effect that the fingerprint/pubkey of the swap
repo is nuked when adding that repo manually.
Internationalised the string "BAD FINGERPRINT" while I was at it.