doc: Clarify use of the 'password' field for user accounts.

Suggested by Alex Sassmannshausen <alex.sassmannshausen@gmail.com>.

* doc/guix.texi (Using the Configuration System): Remove 'password'
  field in the example.
  (User Accounts): Clarify use of the 'password' field, with links to
  the libc and Guile manuals.

doc: Improve acknowledgments.

* doc/guix.texi (Acknowledgments): Expound a bit.
* THANKS: Mention artwork; thank Felipe & Nikita.

gnu: xorg: Add SLiM theme based on work by Felipe López.

* gnu/services/xorg.scm (%artwork-repository, %default-slim-theme,
  %default-slim-theme-name): New variables.
  (slim-service): Add #:theme and #:theme-name parameters.
  [slim.cfg]: Honor #:theme-name.
  Honor #:theme by setting the "SLIM_THEMESDIR" environment variable.
* doc/guix.texi (X Window): Adjust 'slim-service' documentation
  accordingly.  Document '%default-slim-theme' and
  '%default-slim-theme-name'.

activation: Set the firmware search path.

* gnu/build/activation.scm (activate-firmware): New procedure.
* gnu/system.scm (<operating-system>)[firmware]: New field.
  (directory-union): New procedure.
  (%base-firmware): New variable.
  (operating-system-activation-script): Use 'directory-union', and call
  'activate-firmware'.
* doc/guix.texi (operating-system Reference): Document 'firmware'.

doc: Mention 'guix environment' in "Features"; add index entries.

* doc/guix.texi (Features): Add paragraph about 'guix environment'.
  (Build Systems): Add @cindex.
  (Invoking guix environment): Ditto.

doc: Add "GRUB Configuration".

* doc/guix.texi (operating-system Reference): Add xref to "GRUB
  Configuration".
  (GRUB Configuration): New node.

doc: Avoid @indentedblock, which is not supported by Texinfo 4.

Reported by Mark H Weaver.

* doc/guix.texi (Security Updates): Use @quotation instead of
  @indentedblock; the latter is not supported by Texinfo 4.

gexp: Add #:module-path parameter to 'gexp->derivation'.

* guix/gexp.scm (gexp->derivation): Add #:module-path parameter, and
  pass it to 'imported-modules' and 'compiled-modules'.
* doc/guix.texi (G-Expressions): Adjust accordingly.

vm: The 'run-vm' scripts now passes its arguments to QEMU.

* gnu/system/vm.scm (system-qemu-image/shared-store-script): Add "$@" at
  the end of the script.
  (common-qemu-options): Remove trailing newline.
* doc/guix.texi (Invoking guix system): Document it.

vm: Fix 'vm --full-boot' to produce a sufficient disk image.

* gnu/system/vm.scm (system-qemu-image/shared-store): Add
  #:disk-image-size and #:full-boot? parameters and honor them.  Pass
  '#:copy-inputs? full-boot?', and change #:inputs argument.
* guix/scripts/system.scm (system-derivation-for-action): Pass
  #:disk-image-size to 'system-qemu-image/shared-store'.
* doc/guix.texi (Invoking guix system): Mention use of '--image-size' in
  conjunction with '--full-boot'.

vm: Support 'guix system vm --full-boot'.

* gnu/system/vm.scm (system-qemu-image/shared-store-script): Add
  #:full-boot? parameter and honor it.
* guix/scripts/system.scm (system-derivation-for-action): Likewise.
  (perform-action): Likewise.
  (show-help): Document '--full-boot'.
  (%options): Add '--full-boot'.
  (guix-system): Add #:full-boot? argument in call to 'perform-action'.
* doc/guix.texi (Invoking guix system): Document it.

doc: Emphasize the availability of two user interfaces.

* doc/guix.texi (Package Management): Add a word about the two user
  interfaces.

emacs: Add 'guix-prettify'.

* emacs/guix-prettify.el: New file.
* emacs.am (ELFILES): Add it.
* doc/emacs.texi (Emacs Prettify): New node.
* doc/guix.texi (Features): Mention it.

services: xorg: Allow users to specify a list of resolutions.

* gnu/services/xorg.scm (xorg-start-command): Add #:resolutions
  parameter and 'screen-section' procedure.  Use it.
* doc/guix.texi (X Window): Adjust accordingly.

services: xorg: Allow users to specify the drivers to use.

* gnu/services/xorg.scm (xorg-start-command): Add #:drivers parameter.
  Add 'device-section' procedure, and use it in 'xserver.conf'.
* doc/guix.texi (X Window): Document it.

services: Add NTP service.

* gnu/services/networking.scm (ntp-service): New procedure.
* doc/guix.texi (Networking Services): Document it.

packages: Implement grafts.

Thanks to Mark H. Weaver <mhw@netris.org> for insightful discussions
and suggestions.

* guix/packages.scm (<package>)[graft]: New field.
  (patch-and-repack): Invoke 'package-derivation' with #:graft? #f.
  (package-source-derivation): Likewise.  Do not use (%guile-for-build)
  in call to 'patch-and-repack', and we could end up using a grafted
  Guile.
  (expand-input): Likewise, also for 'package-cross-derivation' call.
  (package->bag): Add #:graft? parameter.  Honor it.  Use 'strip-append'
  instead of 'package-full-name'.
  (input-graft, input-cross-graft, bag-grafts, package-grafts): New
  procedures.
  (package-derivation, package-cross-derivation): Add #:graft? parameter
  and honor it.
* gnu/packages/bootstrap.scm (package-with-bootstrap-guile): Add
  recursive call on 'graft'.
* guix/build-system/gnu.scm (package-with-explicit-inputs,
  package-with-extra-configure-variable, static-package): Likewise.
  (gnu-build): Use the ungrafted Guile to avoid full rebuilds.
  (gnu-cross-build): Likewise.
* guix/build-system/cmake.scm (cmake-build): Likewise.
* guix/build-system/glib-or-gtk.scm (glib-or-gtk-build): Likewise.
* guix/build-system/perl.scm (perl-build): Likewise.
* guix/build-system/python.scm (python-build): Likewise.
* guix/build-system/ruby.scm (ruby-build): Likewise.
* guix/build-system/trivial.scm (guile-for-build): Likewise.
* tests/packages.scm ("package-derivation, direct graft",
  "package-cross-derivation, direct graft", "package-grafts,
  indirect grafts", "package-grafts, indirect grafts, cross",
  "package-grafts, indirect grafts, propagated inputs",
  "package-derivation, indirect grafts"): New tests.
  ("bag->derivation", "bag->derivation, cross-compilation"): Wrap in
  'parameterize'.
* doc/guix.texi (Security Updates): New node.
  (Invoking guix build): Document --no-graft.

doc: Add a note about optional GnuTLS dependency.

* README (Requirements): add a note about 'guix download''s GnuTLS dependency.
* doc/guix.texi (Requirements): Likewise.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

doc: Add cross-reference to the gnutls-guile manual.

* doc/guix.texi (Invoking guix download): Add cross-reference to the
  gnutls-guile manual.

guix lint: add the --checkers option.

* guix/scripts/lint.scm: add the "--checkers" option.
* doc/guix.texi (Invoking guix lint): Document it.
* tests/guix-lint.sh: New file
* Makefile.am (SCM_TESTS): Add it.