profiles: xdg-desktop-database: Run the hook when GLib is referenced.

This will pull the latest 'desktop-file-utils' package into the profile
closure, as the 'xdg-mime-database' hook already does.

* guix/profiles.scm (xdg-desktop-database): Run the hook when 'glib' is
referenced.

doc: Update formatting.

* doc/guix.texi (disk-image): Update formatting of "ext4".

Follow-up to 3f4d8a7f66060e93a247797a9bbd2fcbee6922a3.

gnu: Add emacs-emamux.

* gnu/packages/emacs.scm (emacs-emamux): New variable.

Signed-off-by: 宋文武 <iyzsong@member.fsf.org>

build: Add (gnu build file-systems) import.

* gnu/build/vm.scm: Add (gnu build file-systems) import.

guix system: Add "--file-system-type" option.

* guix/scripts/system.scm (process-action): Pass file-system-type to ...
(perform-action): ... here.  Add new keyword argument.  Pass new value to ...
(system-derivation-for-action): ... here.  Add new keyword argument.
Pass new value to system-disk-image.
* doc/guix.texi (disk-image): Document new option.

gnu: gcr: Enable working tests.

* gnu/packages/patches/gcr-disable-failing-tests.patch,
gnu/packages/patches/gcr-fix-collection-tests-to-work-with-gpg-21.patch:
New files.
* gnu/local.mk (dist_patch_DATA): Add patches.
* gnu/packages/gnome.scm (gcr)[source]: Use patches.
[arguments]: Enable tests.

build: Clarify error message when make-iso9660-image fails.

* gnu/build/vm.scm (make-iso9660-image): Clarify error message.

build: Allow specifying volume-uuid with make-iso9660-image.

* gnu/build/file-systems.scm (iso9660-uuid->string): Export.
* gnu/build/vm.scm (make-iso9660-image): Add volume-uuid.

gnu: xfce: Propagate search paths of 'xfce4-panel'.

* gnu/packages/xfce.scm (xfce)[native-search-paths]: New field.

gnu: Add emacs-sparql-mode.

* gnu/packages/emacs.scm (emacs-sparql-mode): New variable.

build: Add iso9660 system image generator.

* build-aux/hydra/gnu-system.scm (qemu-jobs): Add 'iso9660-image .
* gnu/build/vm.scm (make-iso9660-image): New variable.  Export it.
* gnu/system/vm.scm (iso9660-image): New variable.  Use make-iso9660-image.
(system-disk-image): Use iso9660-image.

gnu: Switch guile-cairo and dependents to Guile 2.2 again.

Fixes <https://bugs.gnu.org/27551>.
Reported by Leo Famulari <leo@famulari.name>.

This reinstates the following commits:

  e3ddb1e83 * gnu: guile-cairo: Switch to Guile 2.2.
  ae5c6ef39 * gnu: guile-gnome: Update to 2.16.5.
  0fd8013fc * gnu: guile-rsvg: Update to commit 05c6a2fd.
  66b9183c4 * gnu: guile-lib: Switch to Guile 2.2.

and adds the following changes:

* gnu/bootloader/grub.scm (svg->png): Add 'package->derivation' call for
GUILE-2.2.  Pass #:guile-for-build to 'gexp->derivation'.
* gnu/build/svg.scm (svg->png): Add 'em' and 'ex' to the 'let-values'
form to account for all the values returned by
'rsvg-handle-get-dimensions', which Guile 2.2 does not truncate.

gnu: Add toxic.

* gnu/packages/messaging.scm (toxic): New variable.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

linux-initrd: Add isofs if necessary.

* gnu/system/linux-initrd.scm (base-initrd): Add isofs.

gnu: emacs-guix: Update to 0.3.2.

* gnu/packages/emacs.scm (emacs-guix): Update to 0.3.2.
[arguments]: Add '--with-guix-site-ccache-dir' configure flag, as Guix
installs its .go files separately nowadays.

file-systems: iso9660-uuid->string: Use "-" as separator in the result.

* gnu/build/file-systems.scm (iso9660-uuid->string): Use "-" as separator
in the result.

gnu: beets: Update to 1.4.5.

* gnu/packages/music.scm (beets): Update to 1.4.5.

install: Re-add /bin/sh.

Reported by Divan Santana <divan@santanas.co.za>.
/bin/sh had disappeared in commit
387e175492f960d7d86f34f3b2e43938fa72dbf3.

* gnu/system/install.scm (%installation-services): Add
'special-files-service-type' instance.

gnu: python-vobject: Update to 0.9.5.

* gnu/packages/python.scm (python-vobject, python2-vobject): Update to 0.9.5.

gnu: vdirsyncer: Update to 0.16.0.

* gnu/packages/dav.scm (vdirsyncer): Update to 0.16.0.
[license]: Change to bsd-3.