Add support for require attributes inside children configurations.

svn path=/nixos/trunk/; revision=18820

modules/system/activation/top-level.nix

@@ -41,16 +41,17 @@ let
   # you can provide an easy way to boot the same configuration 
   # as you use, but with another kernel
   # !!! fix this
-  children =
+  children = with pkgs.lib;
     map (childConfig:
-      (import ../../../default.nix {
-        configuration =
-          pkgs.lib.recursiveUpdate childConfig {
+      (import ../../../lib/eval-config.nix {
+        modules = [
+          (recursiveUpdate childConfig {
             boot.loader.grub.device = "";
             # undefined the obsolete name of the previous option.
             boot.grubDevice = pkgs.lib.mkNotdef;
-          };
-      }).system
+          })
+        ] ++ attrByPath ["require"] [] childConfig;
+      }).config.system.build.toplevel
     ) config.nesting.children;