add min-copy-closure, a minimal nix-copy-closure substitute

pkgs/min-copy-closure/receive.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env sh
+cd /nix/store
+while read f ; do
+    test "$f" = "end" && break
+    test -e $f || echo -n $f " "
+done
+mkdir -p /tmp/store
+cd /tmp/store
+cpio -i