stores (typically remote Nix stores mounted via e.g. NFS, or the Nix
store on the NixOS installation CD). Example use:
$ sshfs foo@example.org:/ /mnt
$ NIX_OTHER_STORES=/mnt/nix \
NIX_SUBSTITUTERS=.../copy-from-other-stores.pl \
nix-env -i foo
This will be especially useful for the installation CD since it
doesn't require a manifest for the CD contents.
