hydra: Support a 'subset' argument.

* build-aux/hydra/gnu-system.scm (%core-packages): New variable.
  (%packages-to-cross-build): Make an alias for %CORE-PACKAGES.
  (hydra-jobs): Check for the 'subset' argument, and honor it for values
  "all" and "core".

gnu: linux-libre: Upgrade to 3.11.

* gnu/packages/linux.scm (linux-libre): Upgrade to 3.11.  Add bc as an
  input.

gnu: grub: Add support for building configuration files.

* gnu/packages/grub.scm (<menu-entry>): New record type.
  (grub-configuration-file): New procedure.
* gnu/system/vm.scm (qemu-image): Remove parameters 'linux',
  'linux-arguments', and 'initrd'.  Add 'grub-configuration' parameter.
  Honor them, and remove grub.cfg generation code accordingly.
  (example2): Use `grub-configuration-file', and adjust accordingly.

doc: Add "Data Types and Pattern Matching" to the Coding Style.

* HACKING (Data Types and Pattern Matching): New section.

gnu: Add the 'license:' prefix.

* gnu/packages/glib.scm (itstool): Change 'gpl3+' to 'license:gpl3+'.

gnu: Add itstool.

* gnu/packages/glib.scm (itstool): New variable.

gnu: vm: Add /etc/shadow in the QEMU image.

* gnu/system/vm.scm (qemu-image): Add 'populate' keyword parameter and
  honor it; make it an input.
  (/etc/shadow): New procedure.
  (example2): Call it; build 'populate' script, and pass it to
  'qemu-image'.

gnu: vm: Remove unused 'qemu-image' argument.

* gnu/system/vm.scm (qemu-image): Remove 'boot-expression' parameter,
  superseded by 'linux-arguments'.

gnu: vm: First stab at building a populated QEMU image.

* gnu/packages/linux-initrd.scm (gnu-system-initrd): New variable.
* gnu/system/vm.scm (qemu-image): Add #:linux-arguments parameter.
  [input->name+derivation]: Add case for 'store-path?' items.
  Remove LOADER from `inputs'.

gnu: linux-initrd: Fix creation of /dev/tty nodes.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Make
  /dev/tty.  Change from 'block-special' to 'char-special' for /dev/tty*
  nodes.

gnu: vm: 'qemu-image' populates /dev on the target root file system.

* gnu/system/vm.scm (qemu-image): Use (guix build linux-initrd).  Remove
  'mknod' calls; use 'make-essential-device-nodes' to populate /dev on
  the target image.
* gnu/packages/linux-initrd.scm (qemu-initrd): When /root/dev exists,
  don't call 'make-essential-device-nodes'.

gnu: xorg: Update comment for mesa.

* gnu/packages/xorg.scm (mesa): New compilation trial with 9.2.

gnu: libdrm: Update to 2.4.46.

* gnu/packages/xorg.scm (libdrm): Update to 2.4.46.

hydra: Add Graphviz as an input to the "tarball" job.

* build-aux/hydra/guix.scm (tarball-package): Add GRAPHVIZ to
  `native-inputs'.

hydra: Add Git as an input to the "tarball" job.

* build-aux/hydra/guix.scm (tarball-package): Add `native-inputs' field.

pull: Compile files in the lexicographic order.

* guix/scripts/pull.scm (unpack): Print the name of the file being
  compiled.  Sort the names of files to compile.

build-system/cmake: Fix typo.

* guix/build-system/cmake.scm (default-cmake): Add missing quote.

build-system/gnu: Delay resolution of (@ (gnu packages cmake) cmake).

* guix/build-system/cmake.scm (default-cmake): New procedure.
  (cmake-build): Use it.

substitute-binary: Show the Nar size, when available.

* guix/scripts/substitute-binary.scm (guix-substitute-binary)["--substitute"]:
  Show the Nar size, when available.
* guix/ui.scm (show-what-to-build): Add 'TODO'.

union: Don't traverse sub-directories only found in one element of the union.

This significantly reduces I/O when building profiles, especially with
lots of package-specific sub-directories (such as 'share/emacs/24.3',
'texmf', etc.)

* guix/build/union.scm (union-build)[file-tree](others-have-it?): New
  procedure.  Use it in the 'enter?' parameter of 'file-system-fold';
  change 'skip' parameter accordingly.
* tests/union.scm ("union-build"): Ensure that 'include' is a symlink
  and 'bin' is a directory.