system: Add bindings to configure libc's NSS.

* gnu/system/nss.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* gnu.scm (%public-modules): Add it.
* gnu/system.scm (<operating-system>)[name-service-switch]: New field.
  (etc-directory): Add #:nss parameter and honor it.
  (operating-system-etc-directory): Adjust call accordingly.
* doc/guix.texi (operating-system Reference): Document
  'name-service-switch'.
  (Name Service Switch): New section.

system: Define $ASPELL_CONF in /etc/profile.

* gnu/system.scm (etc-directory)[profile]: Define 'ASPELL_CONF'.

system: Add 'XDG_DATA_DIRS' and 'XDG_CONFIG_DIRS' to /etc/profile.

* gnu/system.scm (etc-directory)[profile]: Set 'XDG_DATA_DIRS' and
  'XDG_CONFIG_DIRS'.

system: Make D-Bus warnings non fatal.

* gnu/system.scm (etc-directory): Add 'DBUS_FATAL_WARNINGS' in PROFILE.

system: Create /etc/emacs/site-start.el.

* gnu/system.scm (emacs-site-file, emacs-site-directory): New
  procedures.
  (etc-directory): Add 'EMACSLOADPATH' setting to PROFILE.  Call
  'emacs-site-directory', and bind its result to /etc/emacs.

system: Add iw to '%base-packages'.

* gnu/system.scm (%base-packages): Add IW.

Merge branch 'master' into 'core-updates'.

system: Add sudo to '%base-packages'.

* gnu/system.scm (%base-packages): Add SUDO.

system: /etc/profile defines 'MANPATH', which includes the global profile.

* gnu/system.scm (etc-directory)[profile]: Set 'MANPATH'.

system: Cleanup bash startup files.

* gnu/system.scm (etc-directory) (bashrc): Rename to 'profile'.
* gnu/system/shadow.scm (default-skeletons): Rename '.bashrc' to
  '.bash_profile'. Don't source /etc/profile.

system: Add 'man-db' to '%base-packages'.

Suggested by Tsutsukakushi on #guix.

* gnu/system.scm (%base-packages): Add MAN-DB.

Revert "system: Add a 'needed-for-boot?' field to 'mapped-device'."

This reverts commit 3b09332adf7ce8e976a4d117a62c586a53af04aa, which
turned out to be a bad idea because we need to have dependency
information between the device-mapping service and the file-system
service that uses it.

system: Add a 'needed-for-boot?' field to 'mapped-device'.

* gnu/system/file-systems.scm (<mapped-device>)[needed-for-boot?]: New
  field.
* gnu/system.scm (operating-system-user-mapped-devices,
  operating-system-boot-mapped-devices): Use it instead of trying to
  guess.  Guessing doesn't work when one refers to a partition using its
  label, for instance.
* doc/guix.texi (Mapped Devices): Document 'needed-for-boot?'.

linux-boot: Load modules and their dependencies, à la 'modprobe'.

* gnu/build/linux-boot.scm: Use (gnu build linux-modules).
  (load-linux-module*): Remove.
  (boot-system): Add #:linux-module-directory parameter.
  [lookup-module]: New procedure.
  Call 'current-module-debugging-port'.  Pass #:lookup-module to
  'load-linux-module*'.  Map LOOKUP-MODULE on LINUX-MODULES.
* gnu/system/linux-initrd.scm (base-initrd): Adjust 'boot-system' call
  accordingly.  Adjust #:modules argument as well.
* gnu/system.scm (operating-system-activation-script)[%modules]: Likewise.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Likewise.

system: Build system-wide locale definitions.

* gnu/system/locale.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* gnu/system.scm (<operating-system>)[locale]: Change the default to
  "en_US.utf8".
  (operating-system-locale-directory): New procecure.
  (operating-system-derivation): Use it.
* doc/guix.texi (Using the Configuration System): Change example locale
  to "fr_FR.utf8".
  (operating-system Reference): Add xref to "Locales".  Document
  'locale-definitions'.
  (Locales): New section.
* po/guix/POTFILES.in: Add gnu/system.scm.

file-systems: 'file-system-needed-for-boot?' always returns #t for "/".

Reported by Nikita Karetnikov.

* gnu/system/file-systems.scm (<file-system>): Rename 'needed-for-boot?'
  accessor to '%file-system-needed-for-boot?'.
  (file-system-needed-for-boot?): New inlinable procedure.
* gnu/system.scm (other-file-system-services)[file-systems]: Rely on
  'file-system-needed-for-boot?' to handle the "/" case.
  (operating-system-initrd-file)[boot-file-systems]: Likewise.

system: Shorten the default label for GRUB entries.

* gnu/system.scm (kernel->grub-label): Shorten entry labels.

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'.

services: Add 'user-unmount-service' as an essential service.

* gnu/services/base.scm (user-unmount-service): New procedure.
* gnu/system.scm (essential-services): Use it.
* gnu/system/install.scm (cow-store-service): Mention it in comment.

system: Define 'INFOPATH' in /etc/profile.

* gnu/system.scm (etc-directory)[bashrc]: Set 'INFOPATH'.