guix package: Reuse FTP connections for subsequent `latest-release' calls.

* guix/gnu-maintenance.scm (latest-release): Add `ftp-close' and
  `ftp-open' keyword parameters.
* guix/scripts/package.scm (ftp-open*): New variable.
  (check-package-freshness): Call `latest-release' with `ftp-open*' and
  a no-op procedure.

gnu-maintenance: `latest-release' closes its connection.

* guix/gnu-maintenance.scm (latest-release): Close CONN before
  returning.

substitute-binary: Directly replace the global `regexp-exec'.

* guix/scripts/substitute-binary.scm (%regexp-exec-mutex, string->uri):
  Remove.
  (regexp-exec): Replace this global binding by a thread-safety wrapper.
  (fields->alist): Remove `with-mutex', and directly alias `recutils->alist'.

substitute-binary: Increase the default timeout.

* guix/scripts/substitute-binary.scm (%fetch-timeout): Set to 5 seconds.

guix refresh: Keep only the newest versions of packages as upgrade candidates.

* guix/scripts/refresh.scm (guix-refresh)[keep-newest]: New procedure.
  Use it to keep only once copy of each package.

gnu-maintenance: Add `doc-description' field to <gnu-package-descriptor>.

* guix/gnu-maintenance.scm (%gsrc-package-list-url): New variable.
  (<gnu-package-descriptor>): Add `doc-description' field.
  (official-gnu-packages)[group-package-fields]: Rename to...
  [read-records]: ... this.  Reverse the result.
  [gsrc-description]: New procedure.
  Add the "description" field to the alist passed to `alist->record'.

records: `recutils->alist' recognizes lines starting with a `+'.

* guix/records.scm (%recutils-plus-rx): New variable.
  (recutils->alist): Use it to read + lines.
* tests/records.scm ("recutils->alist with + lines"): New test.

gnu-maintenance: Use `recutils->alist'.

* guix/gnu-maintenance.scm (official-gnu-packages)[group-package-fields]:
  Rewrite in terms of `recutils->alist'.  Remove `state' parameter.
  Specify "doc-url" and "language" as multiple-value keys in the
  `alist->record' call.

records: `alist->record' supports multiple-field occurrences.

* guix/records.scm (alist->record): Add `multiple-value-keys'
  parameter.  Update docstring, and honor it.
* tests/records.scm ("alist->record"): New record.

records: `recutils->alist' recognizes comments.

* guix/records.scm (%recutils-comment-rx): New variable.
  (recutils->alist): Match comments.
* tests/records.scm ("recutils->alist"): Add comments.

records: Add `recutils->alist' for public consumption.

* guix/records.scm (%recutils-field-rx): New variable.
  (recutils->alist): New procedure, formerly known as `fields->alist'.
* guix/scripts/substitute-binary.scm (fields->alist): Use it.
* tests/records.scm ("recutils->alist"): New test.

Merge branch 'core-updates'

store: Deal with unsupported `setsockopt' operation on GNU/Hurd.

* guix/store.scm (open-connection): Silently ignore ENOPROTOOPT on
  `setsockopt' calls, for the sake of GNU/Hurd.
  Reported by Matthew Lien <bluet@bluet.org> at
  <http://lists.gnu.org/archive/html/bug-guix/2013-07/msg00020.html>.

build-system/gnu: Remove the "debug" output when `strip-binaries?' is #f.

* guix/build-system/gnu.scm (gnu-build, gnu-cross-build): Delete "debug"
  from OUTPUTS when STRIP-BINARIES? is false.
* gnu/packages/cross-base.scm (cross-libc): Leave `outputs' unchanged.
  This reverts commit a4627d4.

build-system/gnu: Write debug files to the "debug" sub-derivation, if any.

* guix/build/gnu-build-system.scm (strip): Add `objcopy-command' keyword
  parameter.
  [debug-output, debug-file-extension]: New variables.
  [debug-file, make-debug-file, add-debug-link]: New procedures.
  [strip-dir]: Use them.

utils: Re-export `alist-cons' and `alist-delete'.

* guix/build/utils.scm: Re-export `alist-cons' and `alist-delete'.

Use `port-sha256' and `open-sha256-port'.

* guix/derivations.scm (derivation-hash): Add comment as to why we keep
  the plain `sha256' call.
* guix/scripts/download.scm (guix-download): Use `port-sha256' instead
  of (compose sha256 get-bytevector-all).
* guix/scripts/refresh.scm (update-package): Likewise.

hash: Add `open-sha256-port'.

* guix/hash.scm (GCRY_MD_SHA256): New macro.
  (sha256): Use it.
  (open-sha256-md, md-write, md-read, md-close, open-sha256-port,
  port-sha256): New procedures.
* tests/hash.scm: New file.
* Makefile.am (SCM_TESTS): Add it.

Move `sha256' to (guix hash).

* guix/utils.scm (sha256): Move to...
* guix/hash.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.
* guix/derivations.scm, guix/scripts/download.scm,
  guix/scripts/hash.scm, guix/scripts/refresh.scm, tests/base32.scm,
  tests/derivations.scm, tests/store.scm: Use (guix hash).

ui: Don't make substituter-related RPCs at all when substitutes are disabled.

Reported by Nikita Karetnikov and Cyril Roelandt.

* guix/ui.scm (show-what-to-build): Call `substitutable-path-info'
  only when USE-SUBSTITUTES? is true.