gnu: linux-libre-headers: Allow cross-compilation.

* gnu/packages/linux.scm (linux-libre-headers): Use (guix build
  gnu-cross-build) and %standard-cross-phases when cross-compiling.

gnu: pkg-config: Export package definition.

* gnu/packages/pkg-config.scm (%pkg-config): Make public.
  Reported by Andreas Enge <andreas@enge.fr>.

gnu: Add pango.

* gnu/packages/gtk.scm (pango): New variable.

gnu: Add harfbuzz.

* gnu/packages/gtk.scm (harfbuzz): New variable.

gnu: Add cairo.

* gnu/packages/gtk.scm (cairo): New variable.

gnu: Add libspectre.

* gnu/packages/ghostscript.scm (libspectre): New variable.

Update `TODO'.

Update upstream Nix sub-module.

* nix-upstream: Update.
* NEWS: Mention multiple-derivation output bug.

derivations: Micro-optimize `derivation-hash'.

* guix/derivations.scm (derivation-hash): Use a UTF-8-encoded string
  output port.  This makes things deterministic, and slightly faster.

gnu: make-bootstrap: Abstract things with `package-with-relocatable-glibc'.

* gnu/packages/make-bootstrap.scm (%glibc-for-bootstrap): Replace with...
  (glibc-for-bootstrap): ... this.  New procedure.
  (%standard-inputs-with-relocatable-glibc): Replace with...
  (package-with-relocatable-glibc): ... this.  New procedure.
  (%static-inputs, %gcc-static, %guile-static): Use it.

gnu: make-bootstrap: Keep Perl as an input only when needed.

* gnu/packages/make-bootstrap.scm (%static-inputs)[coreutils]: Keep Perl
  as an input only if it's an input of COREUTILS.

guix gc: Add `--requisites'.

* guix/scripts/gc.scm (show-help, %options): Add `--requisites'.
  (guix-gc): Handle it.
* doc/guix.texi (Invoking guix gc): Document `--requisites'.
* NEWS: Update.

store: Add `requisites'.

* guix/store.scm (fold-path, requisites): New procedures.
* tests/store.scm ("requisites"): New test.

doc: Describe the build procedure in more detail.

* README (Requirements): Replace "autoreconf" by "bootstrap".
  (Installing Guix from Guix): Augment and update.

gnu: Add GNU gcal.

* gnu/packages/gcal.scm: New file.
* Makefile.am (MODULES): Add it.

Ignore /po/Makevars.template

Fix Guile version checking in the "web" code.

* guix/web.scm (http-fetch): fix Guile version checking. The previous version
would use features from Guile 2.0.9+ when using Guile 2.0.7.

guix refresh: Add '--key-download'.

* guix/gnu-maintenance.scm (download-tarball): Add a 'key-download'
  keyword argument and pass it to 'gnupg-verify*'.  Make
  'archive-type' a keyword argument.
  (package-update): Add a 'key-download' keyword argument.  Pass
  'archive-type' and 'key-download' keyword arguments to
  'download-tarball'.

* guix/gnupg.scm: Import (ice-9 i18n) and (guix ui).
  (gnupg-verify*): Add a 'key-download' keyword argument and adjust
  'gnupg-verify*' to use it.  Make 'server' a keyword argument.

* guix/scripts/refresh.scm (show-help, %options): Add and document
  '--key-download'.
  (update-package): Add a 'key-download' keyword argument and pass it
  to 'package-update'.
  (guix-refresh): Pass 'key-download' to 'update-package'.  Limit
  lines to a maximum of 79 characters.

doc: Mention copyright/license auditing in `HACKING'.

gnu: Add mpg321.

* gnu/packages/mp3.scm (mpg321): New variable.