* Refactoring: Get rid of a few subdirectories in corepkgs/, and some

other simplifications.
* Use <nix/...> to locate the corepkgs.  This allows them to be
  overriden through $NIX_PATH.
* Use bash's pipefail option in the NAR builder so that we don't need
  to create a temporary file.

corepkgs/nar.nix

@@ -0,0 +1,30 @@
+with import <nix/config.nix>;
+
+let
+
+  builder = builtins.toFile "nar.sh"
+    ''
+      export PATH=${nixBinDir}:${coreutils}
+
+      echo "packing ‘$storePath’..."
+      mkdir $out
+      dst=$out/tmp.nar.bz2
+
+      set -o pipefail
+      nix-store --dump "$storePath" | ${bzip2} > $dst
+
+      nix-hash --flat --type $hashAlgo --base32 $dst > $out/narbz2-hash
+
+      mv $out/tmp.nar.bz2 $out/$(cat $out/narbz2-hash).nar.bz2
+    '';
+
+in
+
+{ system, storePath, hashAlgo }:
+
+derivation {
+  name = "nar";
+  builder = shell;
+  args = [ "-e" builder ];
+  inherit system storePath hashAlgo;
+}