The nix-shell fix in 668fef2e4f revealed that we had some --pure tests that incorrectly depended on PATH from config.nix's mkDerivation being overwritten by the caller's PATH. http://hydra.nixos.org/build/49242478
668fef2e4f
"i < argc - 1" should be "i < argc".
nix-shell -A, -p and -i are lightly tested.