* guix/gnu-maintenance.scm (<gnu-release>): Remove.
(coalesce-releases): Move to upstream.scm. Rename to
'coalesce-sources'; adjust callers.
(releases, latest-release): Return <upstream-source> objects instead
of <gnu-release> objects.
(latest-release*, non-emacs-gnu-package?): New procedures.
(gnu-release-archive-types): Remove.
(%gnu-updater): New variable.
(package-update-path, download-tarball, package-update,
update-package-source): Move to...
* guix/upstream.scm: ... here. New file.
* Makefile.am (MODULES): Add it.
* po/guix/POTFILES.in: Replace gnu-maintenance.scm with upstream.scm.
* guix/scripts/refresh.scm (%updaters): New variable.
(update-package): Adjust to new 'package-update' interface.
(guix-refresh): Adjust to new 'package-update-path'. Remove
'false-if-exception' around it.
Ludovic Courtès