web: Factorize `http-get' hackery.

This should fix `substitute-binary --query' on Guile 2.0.5.

* guix/web.scm: New file.
* Makefile.am (MODULES): Add it.
* po/POTFILES.in: Add it.
* guix/gnu-maintenance.scm (http-fetch): Remove.
  (%package-list-url): Turn into a URI.
  (official-gnu-packages): Add #:text? #t to `http-fetch' call.
* guix/scripts/substitute-binary.scm (fetch): Remove `http' case, and
  use `http-fetch' instead.

gnu: wdiff: Update to 1.2.1.

* gnu/packages/wdiff.scm (wdiff): Update to 1.2.1.  Add Texinfo as an input.

gnu: nettle: Update to 2.7.

* gnu/packages/nettle.scm (nettle): Update to 2.7.

gnu: libtasn1: Update to 3.3.

* gnu/packages/gnutls.scm (libtasn1): Update to 3.3.

gnu-maintenance: Optimize `gnu-package?'.

* guix/gnu-maintenance.scm (gnu-package?): Capture a memoizing version
  of `gnu-package?'.

gnu-maintenance: Optimize `release-file'.

* guix/gnu-maintenance.scm (tarball-regexp): Remove.
  (%tarball-rx): New variable.
  (release-file): Adjust to use %TARBALL-RX.

gnu-maintenance: Optimize `latest-release'.

* guix/gnu-maintenance.scm (tarball-regexp, sans-extension,
  release-file): New procedures.
  (%alpha-tarball-rx): New variable.
  (releases): Use them instead of local copies.
  (latest-release): Rewrite to not do a recursive search of all
  versions and instead jump directly to the latest.

Add `guix refresh' and related auto-update tools.

* guix/gnu-maintenance.scm (ftp-server/directory)[quirks]: Add glib.
  (package-update-path, download-tarball, package-update,
  update-package-source): New procedures.
* guix/gnupg.scm, guix/scripts/refresh.scm: New files.
* Makefile.am (MODULES): Add them.
* guix/utils.scm (file-extension): New procedure.

packages: Use `read' and source properties for `package-field-location'.

* guix/packages.scm (package-field-location): Rewrite using `read' and
  source properties.  Change to return #f upon failure.
* tests/packages.scm ("package-field-location"): Check for #f upon failure.
* build-aux/sync-synopses.scm: Adjust accordingly.

utils: Fix column number returned by `source-properties->location'.

* guix/utils.scm (source-properties->location): Use COL, not COL + 1.

gnu: hop: Update hash to match hop-2.4.0.tar.gz, which was modified in place.

* gnu/packages/scheme.scm (hop): Update the hash.

packages: Add `package-field-location'.

* guix/packages.scm (package-field-location): New procedure.
* build-aux/sync-synopses.scm: Use it instead of `package-location'.
* tests/packages.scm ("package-field-location"): New test.

ui: Move macro definitions before any use.

* guix/ui.scm (define-diagnostic, warning, report-error, leave): Move
  definitions before any use.  Reported by Nikita Karetnikov.
  (install-locale): Move back close to `initialize-guix'.

gnu: xorriso: Update to 1.2.8.

* gnu/packages/cdrom.scm (xorriso): Update to 1.2.8.

gnu: smalltalk: Update to 3.2.5.

* gnu/packages/smalltalk.scm (smalltalk): Update to 3.2.5.

gnu: groff: Update to 1.22.2.

* gnu/packages/groff.scm (groff): Update to 1.22.2.

gnu: gprolog: Update to 1.4.3 and download from GNU mirrors

* gnu/packages/gprolog.scm (gprolog): Update to 1.4.3.
  Download from GNU mirrors.

Factorize `download-and-store'.

* guix/download.scm (download-to-store): New procedure.
* guix/scripts/download.scm (fetch-and-store): Remove.
  (guix-download): Use `download-to-store' instead.
* guix/ui.scm (call-with-temporary-output-file): Move to...
* guix/utils.scm (call-with-temporary-output-file): ... here.

Add 'guix hash'.

* guix/scripts/hash.scm: New file.
* Makefile.am (MODULES): Add it.
* po/POTFILES.in: Add it.
* doc/guix.texi (Invoking guix hash): New node.
  (Defining Packages): Add a cross-reference to the 'Invoking guix
  hash' node.

guix download: Add supported formats to '--help'.

* guix/scripts/download.scm (show-help): Add supported formats.