Bump the NixOS version number to 13.07

This is in preparation of making a stable release/branch.  The version
number is <YY>.<MM>, Ubuntu style, denoting the intended release
year/month.  It also has a release codename ("Aardvark").

.version

@@ -1 +1 @@
-0.2
+13.07

modules/installer/tools/nixos-version.sh

@@ -1,2 +1,2 @@
 #! @shell@
-echo @nixosVersion@
+echo "@nixosVersion@ (@nixosCodeName@)"

modules/installer/tools/tools.nix

@@ -55,7 +55,7 @@ let
   nixosVersion = makeProg {
     name = "nixos-version";
     src = ./nixos-version.sh;
-    inherit (config.system) nixosVersion;
+    inherit (config.system) nixosVersion nixosCodeName;
   };
 
   nixosGui = pkgs.xulrunnerWrapper {

modules/misc/version.nix

@@ -16,6 +16,11 @@ with pkgs.lib;
       description = "NixOS version suffix.";
     };
 
+    system.nixosCodeName = mkOption {
+      type = types.uniq types.string;
+      description = "NixOS release code name.";
+    };
+
   };
 
   config = {
@@ -26,6 +31,9 @@ with pkgs.lib;
     system.nixosVersionSuffix =
       mkDefault (if builtins.pathExists ../../.version-suffix then builtins.readFile ../../.version-suffix else "pre-git");
 
+    # Note: code names must only increase in alphabetical order.
+    system.nixosCodeName = "Aardvark";
+
     # Generate /etc/os-release.  See
     # http://0pointer.de/public/systemd-man/os-release.html for the
     # format.
@@ -34,9 +42,9 @@ with pkgs.lib;
           ''
             NAME=NixOS
             ID=nixos
-            VERSION="${config.system.nixosVersion}"
+            VERSION="${config.system.nixosVersion} (${config.system.nixosCodeName})"
             VERSION_ID="${config.system.nixosVersion}"
-            PRETTY_NAME="NixOS ${config.system.nixosVersion}"
+            PRETTY_NAME="NixOS ${config.system.nixosVersion} (${config.system.nixosCodeName})"
             HOME_URL="http://nixos.org/"
           '';
         target = "os-release";