gnu: vm: Fix inputs in 'file-union'.

* gnu/system/vm.scm (file-union): Filter out members of FILES that are
  outputs of INPUTS.

gnu: dmd: Add 'user-accounts' and 'user-groups' fields to <service>.

* gnu/system/shadow.scm (guix-build-accounts): Move to...
* gnu/system/dmd.scm (guix-build-accounts): ... here.
  (<service>)[user-accounts, user-groups]: New fields.
  (guix-service): New #:build-user-id and #:build-accounts parameters.
  Use 'guix-build-accounts' and set the 'user-accounts' and
  'user-groups' fields accordingly.
* gnu/system/vm.scm (system-qemu-image): Remove use of
  'guix-build-accounts'.  Augment ACCOUNTS and GROUPS from what SERVICES
  demand.

gnu: Move /etc/resolv.conf handling to the networking service.

* gnu/system/vm.scm (etc-directory): Remove 'resolv.conf'.
  (system-qemu-image): Use 'static-networking-service' with
  #:name-servers.  Don't populate the image with /etc/resolv.conf.
* gnu/system/dmd.scm (static-networking-service): Add #:name-servers
  parameter.  Use it to populate /etc/resolv.conf.

gnu: vm: Factorize /etc creation.

* gnu/system/vm.scm (expression->derivation-in-linux-vm)[lower-inputs]:
  Move to top-level...
  (lower-inputs): ... here.  New variable.
  (file-union, etc-directory): New procedures.
  (system-qemu-image): Use 'etc-directory'; remove redundant code, and
  register the result of 'etc-directory' as a GC root.

derivations: Use more keyword parameters for 'build-expression->derivation'.

* guix/derivations.scm (build-expression->derivation): Turn 'system' and
  'inputs' into keyword parameters.
  Adjust callers accordingly.
* gnu/system/linux.scm, gnu/system/vm.scm, guix/build-system/cmake.scm,
  guix/build-system/gnu.scm, guix/build-system/perl.scm,
  guix/build-system/python.scm, guix/build-system/trivial.scm,
  guix/download.scm, guix/packages.scm, guix/profiles.scm,
  guix/scripts/pull.scm, tests/derivations.scm, tests/guix-build.sh,
  tests/monads.scm, tests/store.scm, tests/union.scm: Adjust users of
  'build-expression->derivation' and 'derivation-expression'
  accordingly.
* doc/guix.texi (Derivations): Adjust 'build-expression->derivation'
  documentation accordingly.
  (The Store Monad): Likewise for 'derivation-expression'.

Merge branch 'master' into core-updates

Conflicts:
	guix/packages.scm

gnu: vm: Really create a QCOW2-format image.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Pass "-f
  qcow2" to 'qemu-img create'.

gnu: vm: Rewrite helper functions as monadic functions.

* gnu/system/dmd.scm (host-name-service, nscd-service, mingetty-service,
  syslog-service, guix-service, static-networking-service): Rewrite as
  monadic functions.
  (dmd-configuration-file): Use 'text-file' instead of
  'add-text-to-store'.
* gnu/system/grub.scm (grub-configuration-file): Rewrite as a monadic
  function.
* gnu/system/linux.scm (pam-services->directory): Likewise.
* gnu/system/shadow.scm (group-file, passwd-file, guix-build-accounts):
  Likewise.
* gnu/system/vm.scm (expression->derivation-in-linux-vm, qemu-image,
  union, system-qemu-image): Likewise.

gnu: guix: Update to 0.4.

* gnu/packages/package-management.scm (guix): Update to 0.4.
  (guix-0.4): Remove.
* gnu/system/vm.scm (qemu-image, system-qemu-image): Use GUIX instead of
  GUIX-0.4.

gnu: vm: Remove erroneous store reference.

* gnu/system/vm.scm (system-qemu-image): Remove reference from BOOT to
  MINGETTY since MINGETTY may not be valid yet.

gnu: vm: Add more packages to the profile.

* gnu/system/vm.scm (system-qemu-image): Add grep, sed, and Findutils to
  the profile.

gnu: vm: Add a few packages to the default profile.

* gnu/system/vm.scm (system-qemu-image): Add procps, psmisc, and Zile to
  the default profile.  Increase the image size to 550 MiB.

gnu: vm: Set the right permissions and ownership on directories.

* gnu/system/vm.scm (qemu-image): Change the store's mode to #o1775.
  Support 'populate' clauses that specify a UID and GID.
  (system-qemu-image): Make sure /nix/store has owner 'root' and group
  'guixbuild'.  Set the right owner for /home/guest.  Create
  /var/nix/profiles/per-user/{root,guest}.

gnu: vm: Add build users.

* gnu/system/shadow.scm (guix-build-accounts): New procedure.
* gnu/system/vm.scm (system-qemu-image): Use it.  Add the "guixbuild"
  group.
* gnu/system/dmd.scm (guix-service): Add 'builder-group' parameter.
  Pass 'guix-daemon' the '--build-users-group' option.

gnu: vm: Add /etc/{services,protocols,rpc} to the image.

* gnu/system/vm.scm (system-qemu-image): Link
  /etc/{services,protocols,rpc}.  Add net-base as an input.

gnu: vm: Add a 'guest' account.

* gnu/system/vm.scm (system-qemu-image): Add a "guest" user and a
  "users" user group.  Make /home/guest.  Add /etc/group.  Update
  /etc/issue to mention it.

gnu: shadow: Add record type for user groups.

* gnu/system/shadow.scm (<user-group>): New record type.
  (group-file): New procedure.
* gnu/system/vm.scm (system-qemu-image): Use it.

gnu: shadow: Add record type for user accounts.

* gnu/system/shadow.scm (<user-account>): New record type.
  (passwd-file): Use it.
* gnu/system/vm.scm (system-qemu-image): Adjust accordingly.

gnu: vm: Set the default networking route.

* gnu/system/dmd.scm (static-networking-service): Add #:gateway
  parameter and honor it.
* gnu/system/vm.scm (system-qemu-image): Pass #:gateway to
  'static-networking-service'.

Merge branch 'master' into core-updates