Add (gnu) module.

* gnu.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* build-aux/hydra/demo-os.scm: Use (gnu) and strip import list
  accordingly.
* doc/guix.texi (Using the Configuration System): Adjust example
  accordingly.

gnu.scm

@@ -0,0 +1,46 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2014 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu))
+
+;;; Commentary:
+;;;
+;;; This composite module re-exports core parts the (gnu …) public modules.
+;;;
+;;; Code:
+
+(eval-when (eval load compile)
+  (begin
+    (define %public-modules
+      '((gnu system)
+        (gnu system file-systems)
+        (gnu system grub)                         ; 'grub-configuration'
+        (gnu system linux)                        ; 'base-pam-services'
+        (gnu system shadow)                       ; 'user-account'
+        (gnu system linux-initrd)
+        (gnu services)
+        (gnu services base)
+        (gnu packages)
+        (gnu packages base)))
+
+    (for-each (let ((i (module-public-interface (current-module))))
+                (lambda (m)
+                  (module-use! i (resolve-interface m))))
+              %public-modules)))
+
+;;; gnu.scm ends here