gnu: Add express-beta-diversity.

* gnu/packages/bioinformatics.scm (express-beta-diversity): New variable.

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

system: grub: Use a bigger background image.

* gnu/system/grub.scm (grub-background-image): Increase the default
  values of WIDTH and HEIGHT.  After all, it's 2015 already!

gnu: links: Build with libevent.

* gnu/packages/links.scm (links)[inputs]: Add libevent.

gnu: links: Update to 2.12.

* gnu/packages/links.scm (links): Update to 2.12.
  Various whitespace and line length fixes.

gnu: synergy: Upgrade to 1.7.4.

* gnu/packages/synergy.scm (synergy): Upgrade to 1.7.4.

doc: Give an example with an encrypted root partition.

* gnu/system/examples/desktop.tmpl: Add 'mapped-devices' field.
  Use it in 'file-systems'.
* doc/guix.texi (System Installation): Suggest encrypted partitions.
  Give an example of a command sequence.

gnu: xz: Add alternate URL.

Fixes <http://bugs.gnu.org/21784>.

* gnu/packages/compression.scm (xz)[source]: Add alternate URL.

Revert "services: polkit: Use the right executable name for PAM."

This reverts commit 7f39e181dfb34db8f245f3ffafe34eec9cee910d.

Polkit actually uses the name "polkit-1" in calls to 'pam_start'.

gnu: youtube-dl: Minor fixes.

* gnu/packages/video.scm (youtube-dl)[url]: Change to http.
  [description]: Fix capitalization.

gnu: youtube-dl: Update to 2015.11.01.

* gnu/packages/video.scm (youtube-dl): Update to 2015.11.01.

services: Add 'udisks-service'.

* gnu/services/desktop.scm (<udisks-configuration>): New record type.
  (udisks-service-type): New variable.
  (udisks-service): New procedure.
  (%desktop-services): Use it.
* doc/guix.texi (Desktop Services): Document it.

gnu: udisks: Separate HTML documentation.

* gnu/packages/freedesktop.scm (udisks)[outputs]: New field.
  [arguments]: Pass the --with-html-dir configure flag.

gnu: udisks: Mount things under /media.

* gnu/packages/freedesktop.scm (udisks)[arguments]: Add
  --enable-fhs-media.

gnu: udisks: Find the 'mount' command.

* gnu/packages/freedesktop.scm (udisks)[inputs]: Add UTIL-LINUX.
  [arguments]: Add 'set-mount-file-name' phase.

services: 'polkit-service-type' can now be extended.

* gnu/packages/polkit.scm (polkit)[source]: Adjust snippet so that rules
  and actions are looked for under /etc/polkit-1.
* gnu/services/desktop.scm (<polkit-configuration>): New record type.
  (polkit-directory, polkit-etc-files, polkit-setuid-programs): New
  procedures.
  (polkit-service-type)[compose, extend]: New fields.
  (polkit-service): Refine docstring.
  (colord-service-type): Extend POLKIT-SERVICE-TYPE.
  (elogind-configuration-file): Extend POLKIT-SERVICE-TYPE.
* doc/guix.texi (Desktop Services): Update 'polkit-service'
  documentation.

gnu: hurd-headers: Update to 0.7

* gnu/packages/hurd.scm (hurd-headers): Update to version 0.7.

gnu: mig: Update to 1.6

* gnu/packages/hurd.scm (mig): Update to version 1.6.

gnu: gnumach-headers: Update to 1.6

* gnu/packages/hurd.scm (gnumach-headers): Update to version 1.6.

gnu: Remove aarddict.

* gnu/packages/aarddict.scm: Remove file.
* gnu-system.am (GNU_SYSTEM_MODULES): Unregister file.

Merge branch 'dbus-update'