Merge commit staging+systemd into closure-size

Many non-conflict problems weren't (fully) resolved in this commit yet.

nixos/modules/services/system/dbus.nix

@@ -12,7 +12,10 @@ let
 
   configDir = pkgs.stdenv.mkDerivation {
     name = "dbus-conf";
+
     preferLocalBuild = true;
+    allowSubstitutes = false;
+
     buildCommand = ''
       mkdir -p $out
 
@@ -70,6 +73,7 @@ in
       enable = mkOption {
         type = types.bool;
         default = true;
+        internal = true;
         description = ''
           Whether to start the D-Bus message bus daemon, which is
           required by many other system services and applications.

nixos/modules/services/system/nscd.nix

@@ -42,7 +42,10 @@ in
 
   config = mkIf cfg.enable {
 
-    users.extraUsers.nscd.description = "Name service cache daemon user";
+    users.extraUsers.nscd =
+      { isSystemUser = true;
+        description = "Name service cache daemon user";
+      };
 
     systemd.services.nscd =
       { description = "Name Service Cache Daemon";