temporary: Add separate space for temporary overlays

These are intended for temporary fixes to upstream that are
expected to be dropped when incorporated in upstream.

default.nix

@@ -74,16 +74,23 @@ let
   #
   # The naming in this function is misleading but consistent with nixpkgs.
   #
-  # self - final package set (stack fully closed) (called pkgs in all-packages.nix)
+  # self - final package set (stack fully closed) (-> pkgs in all-packages.nix)
   # super - prior package set (stack closed up to us)
-  # res - next package set (stack closed up to and over us) (called self in all-packages.nix_
+  # res - next package set (stack closed up to and over us) (-> self in all-packages.nix)
   #
-  overlaysAlways = [(self: super:
+  overlaysAlways =
     let
-      res = import ./pkgs/all-packages.nix res self;
+      # knot - Feed final and up to and over us overlay results into overlay
+      #
+      # This matche what is done in nixpkgs (see pkgs/top-level/stage.nix).
+      #
+      knot = path: self: super:
+        let res = import path res self; in res;
     in
-      res
-  )];
+      map knot [
+        ./temporary/all-temporary.nix
+        ./pkgs/all-packages.nix
+      ];
 
 in
 

temporary/all-temporary.nix

@@ -0,0 +1,5 @@
+# Temporary stuff (e.g., upstream bug fixes that haven't landed)
+
+self: pkgs: with pkgs; {
+
+}