gnu-maintenance: Add GNOME updater.

* guix/gnu-maintenance.scm (ftp-server/directory)[quirks]: Remove glib.
(false-if-ftp-error): New macro.
(latest-release*): Use it.
(non-emacs-gnu-package?): Rename to...
(pure-gnu-package?): ... this.  Add call to 'gnome-package?'.
(%gnu-updater): Adjust accordingly.
(gnome-package?, latest-gnome-release): New procedures.
(%gnome-updater): New variable.
* guix/scripts/refresh.scm (%updaters): Add %GNOME-UPDATER.
* doc/guix.texi (Invoking guix refresh): Mention it.

refresh: Bail out when asked for a nonexistent updater.

* guix/scripts/refresh.scm (lookup-updater): Call 'leave' when 'find'
returns #f.

refresh: Check updater availability at run time.

This is a followup to b68d2db, which added a check for updaters at
macro-expansion time.  The problem is that, when running 'guix pull',
Guile-JSON is found, so the PyPi updater (say) is added to %UPDATERS,
but then at run time Guile-JSON might be missing.

Reported by orbea on #guix.

* guix/scripts/refresh.scm (maybe-updater): Rewrite as 'syntax-rules'.
Produce code that checks conditions at run time.
(list-updaters): Update docstring.

refresh: Add '--expression'.

* guix/scripts/refresh.scm (%options, show-help): Add --expression.
(guix-refresh): Honor it.
* doc/guix.texi (Invoking guix refresh): Document it.

refresh: Rewrite '--list-dependent' in terms of (guix graph).

* guix/scripts/refresh.scm (all-packages, list-dependents): New
procedures.
(guix-refresh): Use it.

refresh: Avoid non-literal format string.

Reported by Mathieu Lirzin <mthl@gnu.org>.

* guix/scripts/refresh.scm (guix-refresh): Rewrite 'list-dependent?'
  report to avoid nested 'N_' calls.

refresh: Discard PyPI updater when Guile-JSON is missing.

Reported by Sleep_Walker and Mathieu Lirzin <mthl@gnu.org>.

* guix/scripts/refresh.scm (maybe-updater, list-updaters): New macros.
  (%updaters): Use 'list-updaters' instead of 'list'.  Make
  %PYPI-UPDATER conditional.

import: pypi: add updater

* guix/import/pypi.scm (guix-package->pypi-name,
  latest-release): New procedures.
  (%pypi-updater): New variable.
* guix/scripts/refresh.scm (%updaters): Add %PYPI-UPDATER.
* doc/guix.texi (Invoking guix refresh): Mention PyPI

emacs: Add completions for '--type' option of 'refresh' popup.

* guix/scripts/refresh.scm: Export '%updaters'.
* emacs/guix-main.scm (refresh-updater-names): New procedure.
* emacs/guix-base.el (guix-refresh-updater-names): New function.
* emacs/guix-read.el (guix-read-refresh-updater-names,
  guix-read-refresh-updater-names-string): New functions.
* emacs/guix-command.el (guix-command-improve-refresh-argument): Use
  'guix-read-refresh-updater-names-string'.

Merge branch 'master' into dbus-update

refresh: Support comma-separated updater types.

* guix/scripts/refresh.scm (%options): Handle comma-separated types for
  '--type' option.
  (guix-refresh): Adjust accordingly.
  (show-help): Likewise.
* doc/guix.texi (Invoking guix refresh): Document it.

refresh: Add '--list-updaters' option.

* guix/scripts/refresh.scm (list-updaters-and-exit): New procedure.
  (%options, show-help): Add '--list-updaters' option.
* doc/guix.texi (Invoking guix refresh): Document it.

Merge branch 'master' into dbus-update

import: cran: Add updater.

* guix/import/cran.scm (downloads->url, nodes->text): New procedures.
  (cran-sxml->sexp): Use them.  Remove equivalent local code.
  (latest-release, cran-package?): New procedures.
  (%cran-updater): New variable.
* guix/scripts/refresh.scm (%updaters): Add %CRAN-UPDATER.
* doc/guix.texi (Invoking guix refresh): Mention CRAN.

refresh: Remove exception catch-all.

* guix/scripts/refresh.scm (update-package): Remove 'catch #t'.

refresh: Add '--type' option.

* guix/scripts/refresh.scm (%options, show-help): Add --type.
  (lookup-updater): New procedure.
  (update-package): Add 'updaters' parameter and honor it.
  (guix-refresh)[options->updaters]: New procedure.
  Use it, and honor --type.

import: elpa: Add updater.

* guix/import/elpa.scm (latest-release, package-from-gnu.org?): New
  procedures.
  (%elpa-updater): New variable.
* guix/scripts/refresh.scm (%updaters): Add %ELPA-UPDATER.

gnu-maintenance: Generalize, leading to (guix upstream).

* 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.

Merge branch 'master' into core-updates

Add (guix scripts).

* guix/ui.scm: Add missing copyright lines.
  (args-fold*, environment-build-options, %default-argument-handler,
  parse-command-line): Move to ...
* guix/scripts.scm: ...here.  New file.
* guix/scripts/archive.scm: Use it.
* guix/scripts/build.scm: Likewise.
* guix/scripts/download.scm: Likewise.
* guix/scripts/edit.scm: Likewise.
* guix/scripts/environment.scm: Likewise.
* guix/scripts/gc.scm: Likewise.
* guix/scripts/graph.scm: Likewise.
* guix/scripts/hash.scm: Likewise.
* guix/scripts/import/cpan.scm: Likewise.
* guix/scripts/import/cran.scm: Likewise.
* guix/scripts/import/elpa.scm: Likewise.
* guix/scripts/import/gem.scm: Likewise.
* guix/scripts/import/gnu.scm: Likewise.
* guix/scripts/import/hackage.scm: Likewise.
* guix/scripts/import/nix.scm: Likewise.
* guix/scripts/import/pypi.scm: Likewise.
* guix/scripts/lint.scm: Likewise.
* guix/scripts/package.scm: Likewise.
* guix/scripts/publish.scm: Likewise.
* guix/scripts/pull.scm: Likewise.
* guix/scripts/refresh.scm: Likewise.
* guix/scripts/size.scm: Likewise.
* guix/scripts/system.scm: Likewise.
* tests/ui.scm (with-environment-variable, "parse-command-line",
  "parse-command-line and --no options"): Move to ...
* tests/scripts.scm: ...here.  New file.
* Makefile.am (MODULES): Add guix/scripts.scm.
  (SCM_TESTS): Add tests/scripts.scm.
* po/guix/POTFILES.in: Add guix/scripts.scm.