While this method is new and nar-sha256 ExtIDs are currently available
only for new visits, it is fundamentally more reliable than the other
methods, which is why it comes first.
* guix/lint.scm (check-archival)[lookup-by-nar-hash]: New procedure.
Call ‘lookup-by-nar-hash’ before the other lookup methods.
* tests/lint.scm ("archival: content available")
("archival: content unavailable but disarchive available")
("archival: missing revision")
("archival: revision available"): Add a 404 response corresponding to
the ‘lookup-external-id’ request.
* tests/lint.scm ("archival: nar-sha256 extid available"): New test.
Change-Id: I4a81d6e022a3b72e6484726549d7fbae627f8e73
