gnu: xorg: Fix http mirror and uncomment xcb packages.

* guix/download.scm (%mirrors): Fix main http mirror address.
* gnu/packages/xorg.scm (libpthread-stubs, libxcb, xcb-proto): Uncomment
     and add licenses.

utils: Add a #:follow-symlinks? parameter to `copy-recursively'.

* guix/build/utils.scm (copy-recursively): Turn `log' into a keyword
  parameter.  Add the `follow-symlinks?' parameter and honor it.

utils: Add `delete-file-recursively'.

* guix/build/utils.scm (delete-file-recursively): New procedure.

Merge branch 'master' into core-updates

Conflicts:
	Makefile.am
	guix/scripts/gc.scm
	guix/scripts/package.scm
	guix/ui.scm
	tests/guix-package.sh

guix: build: Add "share/pkgconfig" to PKG_CONFIG_PATH, as used by xorg.

* guix/build/gnu-build-system.scm (set-paths): Add "share/pkgconfig"
     to PKG_CONFIG_PATH.

Add (guix build-system perl).

* guix/build-system/perl.scm, guix/build/perl-build-system.scm: New files.
* Makefile.am (MODULES): Add them.
* guix/build-system/gnu.scm (standard-inputs): Make public.

download: Add CPAN mirrors.

* guix/download.scm (%mirrors)[cpan]: New URLs.

ui: Factorize `read/eval-package-expression'.

* guix/scripts/package.scm (read/eval-package-expression): Move to...
* guix/ui.scm (read/eval-package-expression): ... here.
* guix/scripts/build.scm (derivations-from-package-expressions): Use it.

guix package: Add `--install-from-expression'.

* guix/scripts/package.scm (read/eval-package-expression): New
  procedure.
  (show-help): Add `-e'.
  (%options): Likewise.
  (guix-package)[process-actions]: Handle ('install . p) pairs, where P
  is a package.
* tests/guix-package.sh: Add `boot_make_drv'.  Use `-i $boot_make_drv'
  once, and then use `-e $boot_make'.
* doc/guix.texi (Invoking guix package): Document `-e'.

guix gc: Add `--references' and `--referrers'.

* guix/scripts/gc.scm (show-help): Update.
  (%options): Add `--references' and `--referrers'.
  (guix-gc)[symlink-target, store-directory]: New procedures.
  Handle the `list-references' and `list-referrers' actions.
* tests/guix-gc.sh: Add tests for `--references'.
* doc/guix.texi (Invoking guix gc): Document `--references' and
  `--referrers'.

store: Add queries for references & co.

* guix/store.scm (operation-id)[query-valid-derivers]: New value.
  (references, referrers, valid-derivers, query-derivation-outputs): New
  procedures.
* tests/store.scm ("references", "derivers"): New tests.

pull: Distinguish "already up to date" from "updated".

* guix/ui.scm (show-what-to-build): Return (length req*).
* guix/scripts/pull.scm (guix-pull): Print an "already up to date"
  message when there's nothing to build.

pull: Build (guix build download) first, because of the (gnutls) autoload.

* guix/scripts/pull.scm (unpack): Build (guix build download) first, as
  done in 855a8ad71def2ebc594ed32c57bda0ca4e13d91c.
  Reported by Andreas Enge <andreas@enge.fr>.

Add "guix pull".

* guix/scripts/pull.scm: New file.
* Makefile.am (MODULES): Add it.
* doc/guix.texi (Invoking guix pull): New node.
  (Invoking guix package): Add cross-ref to it.
* guix/ui.scm (config-directory): New procedure.
* scripts/guix.in: When `GUIX_UNINSTALLED' is undefined, add
  $XDG_CONFIG_HOME/guix/latest to the search path.
* po/POTFILES.in: Add guix/scripts/pull.scm.

ui: Factorize `show-what-to-build'.

* guix/scripts/package.scm (guix-package)[show-what-to-build]: Move to..
* guix/ui.scm (show-what-to-build): ... here.  Add a `store'
  parameter'.  Adjust callers.
* guix/scripts/build.scm (guix-build): Use it.  Remove `req' and `req*'
  variables.

ui: Add temporary file handling and atomic symlink switch.

* guix/scripts/download.scm (call-with-temporary-output-file): Move to
  ui.scm.
* guix/scripts/package.scm (switch-symlinks): Likewise.
* guix/ui.scm (call-with-temporary-output-file, switch-symlinks): New
  procedures.

download: Adjust to `http-get*' deprecation.

* guix/build/download.scm (http-fetch): Adjust to use #:streaming? when
  using Guile 2.0.8+.

derivations: Add a search path parameter for module derivations.

* guix/derivations.scm (imported-modules, compiled-modules): Add a
  `module-path' parameter.  Use it instead of %LOAD-PATH.

store: Add the `%daemon-socket-file' parameter.

* guix/store.scm (%daemon-socket-file): New variable.
  (open-connection): Use it as the default value for FILE.

scripts: Remove hyphen in the command name shown by `--version'.

* guix/scripts/build.scm (%options): Remove hyphen from the name passed
  to `show-version-and-exit'.
* guix/scripts/download.scm (%options): Likewise.
* guix/scripts/gc.scm (%options): Likewise.
* guix/scripts/import.scm (%options): Likewise.
* guix/scripts/package.scm (%options): Likewise.