gnu: linux-libre: Update to 4.12.9.

* gnu/packages/linux.scm (%linux-libre-version): Update to 4.12.9.
(%linux-libre-hash): Update hash.

gnu: linux-libre@4.9: Update to 4.9.45.

* gnu/packages/linux.scm (linux-libre-4.9): Update to 4.9.45.

gnu: linux-libre@4.4: Update to 4.4.84.

* gnu/packages/linux.scm (linux-libre-4.4): Update to 4.4.84.

gnu: go: Update to 1.9.

* gnu/packages/golang.scm (go-1.8): Replace with ...
(go-1.9): ... new variable.
[arguments]: Adjust the pre-build phase accordingly.

gnu: Add draft of gdm service.

* gnu/services/xorg.scm (%gdm-accounts, <gdm-configuration>)
(gdm-etc-service, gdm-pam-service, gdm-shepherd-service, gdm-service-programs)
(gdm-service-type, gdm-service): New public variables.  Not yet working.

gnu: services: Log debug messages to /var/log/debug.

* gnu/services/base.scm (%default-syslog.conf): Create a /var/log/debug with
  messages logged to syslog at debug level.

gnu: gdm: Fix environment of worker processes and sessions.

* gnu/packages/gnome.scm (gdm): Get X server path from GDM_X_SERVER
environment variable, and make sure this variable is propagated to internal
sub-processes.  Launch sessions with a reasonable XDG_CONFIG_DIRS setting.
Get the custom GDM conf from the current system's profile.

gnu: gdm: Use proper elogind check, and wrap environment.

* gnu/packages/gnome.scm (gdm): Use glib-or-gtk-build-system to make sure the
schemas are available to GDM.  Install gdm to /bin to make this happen.  Use a
proper elogind check.

gnu: gdm: Look for sessions in /run/current-system.

* gnu/packages/gnome.scm (gdm): Fix search paths for system sessions.  Use
  /var as localstatedir.  Set a more sensible default path for user sessions.

gnu: services: Refactor to separate X and startx wrappers.

* gnu/services/xorg.scm (xorg-wrapper): New public function.
(xorg-start-command): Use xorg-wrapper.

gnu: Add AccountsService service to desktop services.

* doc/guix.texi (Desktop Services): Add accountsservice-service.
* gnu/services/desktop.scm (%accountsservice-activation):
(accountsservice-service-type): New public variables.
(%desktop-services): Add accountsservice-service.

gnu: accountsservice: Properly reference shadow.

* gnu/packages/freedesktop.scm (accountsservice): Fix references to binaries
  provided by the shadow package.

gnu: parallel: Update to 20170822.

* gnu/packages/parallel.scm (parallel): Update to 20170822.

gnu: yoshimi: Update to 1.5.3.

* gnu/packages/music.scm (yoshimi): Update to 1.5.3.

gnu: zynaddsubfx: Update to 3.0.2.

* gnu/packages/music.scm (zynaddsubfx): Update to 3.0.2.

gnu: guile-xcb: Update source URL.

* gnu/packages/guile-wm.scm (guile-xcb)[source]: Use archived tarball URL.

graft: Correctly replace references near the end of the scan buffer.

Fixes <http://bugs.gnu.org/28212>.
Reported by Leo Famulari <leo@famulari.name>.

* guix/build/graft.scm (replace-store-references): When I >= END, check
whether WRITTEN > END and call 'get-bytevector-n!' when it is.
* tests/grafts.scm (buffer-size): New variable.
("replace-store-references, <http://bugs.gnu.org/28212>"): New test.

Revert "graph: Provide access to the package record in the emit functions."

This reverts commit 5d7e8543659874682b618bba799ba7cd6ffce554, which
broke 'tests/graph.scm' and broke node types not related to <package>
objects, such as '%reference-node-type'.

gnu: font-mathjax: Move to javascript.scm.

This avoids cross-module top-level references.

* gnu/packages/fonts.scm (font-mathjax): Move to...
* gnu/packages/javascript.scm (font-mathjax): ... here.  New variable.

gnu: font-go: Remove reference to 'go-1.4'.

This avoids circular references at the top level.

* gnu/packages/fonts.scm (font-go)[license]: Remove reference to
GO-1.4.