Adding back passthru functionality

svn path=/nixos/branches/modular-nixos/; revision=16237

modules/misc/passthru.nix

@@ -0,0 +1,21 @@
+# This module allows you to export something from configuration
+# Use case: export kernel source expression for ease of configuring 
+
+{config, pkgs, ...}:
+
+let 
+
+options = {
+  passthru = pkgs.lib.mkOption {
+    description = ''
+      This attribute set will be exported as a system attribute.
+      You can put whatever you want here.
+    '';
+  };
+};
+
+in 
+
+{
+  require = options;
+}

modules/module-list.nix

@@ -16,6 +16,7 @@
   ./misc/assertions.nix
   ./misc/ids.nix
   ./misc/locate.nix
+  ./misc/passthru.nix
   ./programs/bash/bash.nix
   ./programs/info.nix
   ./programs/pwdutils/pwdutils.nix