vm: Provide a root partition for the freestanding VM image.

Fixes a regression introduced in 83bcd0b.

* gnu/system/vm.scm (system-qemu-image): Override the 'file-systems'
  field of OS.  Add #:file-system-type parameter and honor it.

vm: Make root file system type a parameter, and default to ext4.

* gnu/system/vm.scm (qemu-image): Add #:file-system-type parameter.
  Pass it to 'initialize-hard-disk'.
* guix/build/linux-initrd.scm (mount-root-file-system): Always honor
  TYPE.
  (boot-system): Change #:root-fs-type to default to "ext4".  Update
  docstring.
* guix/build/vm.scm (initialize-hard-disk): Remove #:mkfs parameter; add
  #:file-system-type.  Adjust 'mkfs' invocation and 'mount' call to
  honor #:file-system-type.

doc: Minor improvements in "G-Expressions".

* doc/guix.texi (G-Expressions): Show coreutils version number in store
  file name.  Add xref to "Derivations", in documentation of
  'gexp->derivation'.  Fix typo.

gnu: Add diffstat.

* gnu/packages/version-control.scm (diffstat): New variable.

ftp-client: Add missing CR in "USER" command.

* guix/ftp-client.scm (%ftp-login): Add #\return before #\newline.
  Fixes access to some FTP servers, such as
  ftp://invisible-island.net ("ProFTPD 1.3.4a Server").

system: Add first-class file system declarations.

* gnu/system.scm (<operating-system>)[initrd]: Default to
  'qemu-initrd'.
  (<file-system>): New record type.
  (operating-system-root-file-system): New procedure.
  (operating-system-derivation): Take the device name for GRUB from
  'operating-system-root-file-system'.  Pass the
  'operating-system-initrd' procedure the list of boot file systems.
* gnu/system/linux-initrd.scm (file-system->spec): New procedure.
  (qemu-initrd): Add 'file-systems' parameter, and remove #:mounts
  parameter.
  [file-system-type-predicate]: New procedure.
  [linux-modules]: Use it.
  Adjust #:mounts argument in 'boot-system' call.
  (gnu-system-initrd): Remove.
* gnu/system/vm.scm (%linux-vm-file-systems): New variable.
  (expression->derivation-in-linux-vm): Adjust call to 'qemu-initrd'.
  (virtualized-operating-system): New procedure.
  (system-qemu-image/shared-store-script)[initrd]: Remove.  Use
  'virtualized-operating-system'.  Get the 'initrd' file from OS-DRV.
* guix/build/linux-initrd.scm (mount-qemu-smb-share, mount-qemu-9p):
  Remove.
  (MS_RDONLY, MS_BIND): New global variables.
  (bind-mount): Remove local 'MS_BIND' definition.
  (mount-root-file-system): New procedure, with code formerly in
  'boot-system'.
  (mount-file-system): New procedure.
  (boot-system): Add #:root-fs-type parameter.  Remove 'MS_RDONLY' local
  variable.  Use 'mount-root-file-system' and 'mount-file-system'.
* doc/guix.texi (Using the Configuration System): Add 'file-system'
  declaration.

gnu: Add missing copyright line

* gnu/packages/maths.scm: Add copyright line missing from 3de01d3.

gnu: petsc: Add input superlu.

* gnu/packages/maths.scm (petsc): Configure with superlu support.

gnu: Add superlu

* gnu/packages/maths.scm (superlu): New variable

gnu: qemu: Upgrade to 2.0.0.

* gnu/packages/qemu.scm (qemu-headless): Upgrade to 2.0.0.

download: Rewrite using gexps.

* guix/download.scm (gnutls-derivation): Remove.
  (gnutls-package): New procedure.
  (url-fetch): Rewrite using 'gexp->derivation'.

monads, gexp: Remove unintended dependency on (gnu packages …).

* guix/gexp.scm (gexp->derivation, gexp->script): Use 'default-guile'
  instead of an explicit reference to 'guile-final'.
  (default-guile): New procedure.
* guix/monads.scm (run-with-store)[default-guile]: New procedure.
  Use it.

gexp: Add support for 'origin?' objects in 'ungexp' forms.

* guix/gexp.scm (lower-inputs, gexp-inputs, gexp->sexp,
  canonicalize-reference): Add 'origin?' case.
* guix/monads.scm (origin->derivation): New procedure.
* tests/gexp.scm ("one input origin"): New test.

system: Add 'sudo' to the setuid programs, and handle /etc/sudoers.

* gnu/system.scm (<operating-system>)[groups]: Change default to just
  the 'root' group.
  [sudoers]: New field.
  (etc-directory): Add #:sudoers parameter.  Add 'sudoers' to the
  file union.
  (operating-system-etc-directory): Pass #:sudoers to 'etc-directory'.
  (%setuid-programs): Add 'sudo'.
  (%sudoers-specification): New variable.
* gnu/system/linux.scm (base-pam-services): Add 'sudo'.
* build-aux/hydra/demo-os.scm: Add 'groups' field; add 'guest' to the
  'wheel' group.

gnu: Add petsc

* gnu/packages/maths.scm (petsc): New variable.
  (petsc-complex): New variable.
* gnu/packages/patches/petsc-fix-threadcomm.patch: New patch.
* gnu-system.am (dist_patch_DATA): Add it.

gnu: Add abbaye.

* gnu/packages/games.scm (abbaye): New variable.

gnu: Propagate necessary inputs for sdl-image.

* gnu/packages/sdl.scm (sdl-image): Propagate jpeg, png, and tiff
  libraries.

gexp: Add pretty printer.

* guix/gexp.scm (write-gexp): New procedure.
  <top level>: Add call to 'set-record-type-printer!'.

gnu: Add sudo.

* gnu/packages/admin.scm (sudo): New variable.

system: Add support for setuid binaries.

* gnu/system.scm (<operating-system>)[pam-services, setuid-programs]:
  New fields.
  (etc-directory)[bashrc]: Prepend /run/setuid-programs to $PATH.
  (operating-system-etc-directory): Honor
  'operating-system-pam-services'.
  (%setuid-programs): New variable.
  (operating-system-boot-script): Add (guix build utils) to the set of
  imported modules.  Call 'activate-setuid-programs' in boot script.
* gnu/system/linux.scm (base-pam-services): New procedure.
* guix/build/activation.scm (%setuid-directory): New variable.
  (activate-setuid-programs): New procedure.
* build-aux/hydra/demo-os.scm: Add 'pam-services' field.