Fixes <http://bugs.gnu.org/19840>.
Reported by Ricardo Wurmus <rekado@elephly.net>.
* guix/build/download.scm: On Guile 2.0.11 or earlier, redefine the http
"Location" header to accept relative URIs.
(resolve-uri-reference): New exported procedure.
(http-fetch): Use 'resolve-uri-reference' to resolve redirections.
* guix/http-client.scm (http-fetch): Use 'resolve-uri-reference'
* guix/http-client.scm (&http-get-error): New condition type.
(http-fetch): Raise it instead of using 'error'.
* guix/scripts/substitute-binary.scm (fetch) <http>: Wrap body into
'guard' form; gracefully handle 'http-get-error?' conditions.
This fixes Guile version comparisons when (version) has a
vendor-specific suffix.
Reported by Andreas Enge <andreas@enge.fr>.
* guix/utils.scm (guile-version>?): New procedure.
* tests/utils.scm ("guile-version>? 1.8", "guile-version>? 10.5"): New
tests.
* guix/scripts/substitute-binary.scm (fetch, progress-report-port): Use
`guile-version>?' instead of `version>?'.
* guix/http-client.scm (when-guile<=2.0.5, http-fetch): Likewise.
Ludovic Courtès