ef4f5ba85e
This prevents some duplicate evaluation in nix-env and nix-instantiate. Also, when traversing ~/.nix-defexpr, only read regular files with the extension .nix. Previously it was reading files like .../channels/binary-caches/<name>. The only reason this didn't cause problems is pure luck (namely, <name> shadows an actual Nix expression, the binary-caches files happen to be syntactically valid Nix expressions, and we iterate over the directory contents in just the right order).
Nix is a purely functional package manager. For installation and usage instructions, please read the manual, which can be found in `docs/manual/manual.html', and additionally at the Nix website at <http://nixos.org/>. Acknowledgments This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.OpenSSL.org/).