gnu: Fix invalid `license' fields.

* gnu/packages/acl.scm (acl): Change `license' field to refer to the
  `license' objects.
* gnu/packages/attr.scm (attr): Likewise.
* gnu/packages/compression.scm (xz): Likewise.
* gnu/packages/global.scm (global): Likewise.
* gnu/packages/linux.scm (linux-libre-headers): Likewise.

gnu/packages/acl.scm

@@ -63,4 +63,4 @@
      "Library and tools for manipulating access control lists")
     (description
      "Library and tools for manipulating access control lists.")
-    (license '(gpl2+ lgpl2.1+))))
+    (license (list gpl2+ lgpl2.1+))))

gnu/packages/attr.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2012 Nikita Karetnikov <nikita@karetnikov.org>
-;;; Copyright © 2012 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -74,4 +74,4 @@
      "Library and tools for manipulating extended attributes")
     (description
      "Portable library and tools for manipulating extended attributes.")
-    (license '(gpl2+ lgpl2.1+))))
+    (license (list gpl2+ lgpl2.1+))))

gnu/packages/compression.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -171,7 +171,7 @@ been modified quite a lot to be suitable for XZ Utils.  The primary
 compression algorithm is currently LZMA2, which is used inside the .xz
 container format.  With typical files, XZ Utils create 30 % smaller output
 than gzip and 15 % smaller output than bzip2.")
-   (license '(license:gpl2+ license:lgpl2.1+))              ; bits of both
+   (license (list license:gpl2+ license:lgpl2.1+)) ; bits of both
    (home-page "http://tukaani.org/xz/")))
 
 (define-public lzo

gnu/packages/global.scm

@@ -55,4 +55,4 @@ subdirectories, many #ifdef and many main() functions.  It is similar
 to ctags or etags but is different from them at the point of
 independence of any editor.  It runs on a UNIX (POSIX) compatible
 operating system like GNU and BSD.")
-    (license "GPLv3+")))
+    (license gpl3+)))

gnu/packages/linux.scm

@@ -80,7 +80,7 @@
        #:tests? #f))
     (synopsis "GNU Linux-Libre kernel headers")
     (description "Headers of the Linux-Libre kernel.")
-    (license "GPLv2")
+    (license gpl2)
     (home-page "http://www.gnu.org/software/linux-libre/"))))
 
 (define-public linux-pam