system: Always create /var/empty.

* guix/build/install.scm (directives): Add /var/empty.

system: Separate the activation script from the boot script.

* gnu/system.scm (operating-system-activation-script): New procedure,
  containing most of the former 'operating-system-boot-script'.
  (operating-system-boot-script): Call it, and 'primitive-load' its
  result.
* guix/build/activation.scm (%booted-system): Remove.
  (activate-current-system): Remove #:boot? parameter and related code.

gnu: Add lzop.

* gnu/packages/compression.scm (lzop): New variable.

vm: Disable QEMU networking in the disk image initrd.

* gnu/system/linux-initrd.scm (qemu-initrd): Add #:qemu-networking?
  parameter and honor it.
* gnu/system/vm.scm (system-disk-image): Pass #:qemu-networking #f.

download: Enlarge your receive buffer.

* guix/build/download.scm (open-connection-for-uri): Remove call to
  'setsockopt'.
* guix/http-client.scm (open-socket-for-uri)[rmem-max, buffer-size]: New
  variables.  Add call to 'setsockopt'.

guix system: Add 'disk-image' action.

* guix/scripts/system.scm (show-help): Add 'disk-image'.
  (guix-system)[parse-options]: Support 'disk-image' action.
  [option-arguments]: Likewise.
  Handle the 'disk-image' action.
* doc/guix.texi (Invoking guix system): Document 'disk-image'.

vm: Add 'system-disk-image'.

* gnu/system/vm.scm (system-disk-image): New procedure.

Add (gnu) module.

* gnu.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* build-aux/hydra/demo-os.scm: Use (gnu) and strip import list
  accordingly.
* doc/guix.texi (Using the Configuration System): Adjust example
  accordingly.

vm: Use a para-virtualized disk when creating an image.

* guix/build/vm.scm (load-in-linux-vm): When MAKE-DISK-IMAGE?, use
  '-drive ...,if=virtio' for better performance.
* gnu/system/vm.scm (qemu-image): Use /dev/vda instead of /dev/sda.

vm: Make the image format a parameter.

* guix/build/vm.scm (load-in-linux-vm): Add #:disk-image-format
  parameter; add 'image-file' variable.  Honor DISK-IMAGE-FORMAT.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Add
  #:disk-image-format parameter, and honor it.
  (qemu-image): Likewise.

linux-initrd: Build /dev/loop* nodes.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Build
  /dev/loop[0-7].

gnu: imagemagick: Upgrade to 6.8.9-0.

* gnu/packages/imagemagick.scm (imagemagick): Upgrade to 6.8.9-0.

gnu: perl-io-tty: Upgrade to 1.11.

* gnu/packages/perl.scm (perl-io-tty): Upgrade to 1.11.

guix: download: Update imagemagick mirrors.

* guix/download.scm (%mirrors)[imagemagick]: Update and add the legacy
    subdirectory of the main site as a last resort.

build: Fix builds without --with-libgcrypt-prefix nor --with-libgcrypt-libdir.

Reported by Manolis Ragkousis <manolis837@gmail.com>.
Fixes a regression introduced in 14af289.

Before this commit, ./configure would leave LIBGCRYPT_PREFIX and
LIBGCRYPT_LIBDIR undefined, leading to LIBGCRYPT_LIBS="-L -lgcrypt" and
thus to a link failure.

* configure.ac: Make sure $LIBGCRYPT_PREFIX and $LIBGCRYPT_LIBDIR are
  never empty.

vm: Modularize build-side code.

* guix/build/install.scm (install-grub): Call 'error' if 'system*'
  returns non-zero.
* guix/build/vm.scm (initialize-partition-table): Make 'partition-size'
  a positional parameter.  Call 'error' when 'system*' returns
  non-zero'.
  (format-partition, initialize-root-partition): New procedures.
  (initialize-hard-disk): Use them.

vm: Remove misleading comment.

* guix/build/vm.scm (load-in-linux-vm): Remove misleading comment.

gnu: Add wpa_supplicant.

* gnu/packages/admin.scm (wpa-supplicant): New variable.

store: Flush the output when the build process emits '\r'.

This allows progress reports emitted by 'substitute-binary' to be
correctly displayed.

* guix/store.scm (%newlines): New variable.
  (process-stderr) <%stderr-next>: Flush (current-build-output-port)
  when S contains one of %NEWLINES.

Augment (guix).

* guix.scm (%public-modules): Add 'monads' and 'gexp'.