* Allow '<nixexpr>' syntax to be used in nix-instantiate, nix-build

and nix-env, e.g.,

  $ nix-env -f '<nixpkgs>' -i patchelf

  or

  $ nix-build '<nixos/tests>' -A login.test

src/nix-instantiate/nix-instantiate.cc

@@ -138,8 +138,7 @@ void run(Strings args)
     }
 
     foreach (Strings::iterator, i, files) {
-        Path path = absPath(*i);
-        Expr * e = state.parseExprFromFile(path);
+        Expr * e = state.parseExprFromFile(lookupFileArg(state, *i));
         processExpr(state, attrPaths, parseOnly, strict, autoArgs,
             evalOnly, xmlOutput, xmlOutputSourceLocation, e);
     }