* guix/lint.scm (check-archival): New procedure. (%network-dependent-checkers): Add 'archival' checker. * tests/lint.scm ("archival: missing content") ("archival: content available") ("archival: missing revision") ("archival: revision available") ("archival: rate limit reached"): New tests. * doc/guix.texi (Invoking guix lint): Document it.