* Check for duplicate attribute names / function arguments. `make

check' now succeeds :-)
* An attribute set such as `{ foo = { enable = true; };
  foo.port = 23; }' now parses.  It was previously rejected, but I'm
  too lazy to implement the check.  (The only reason to reject it is
  that the reverse, `{ foo.port = 23; foo = { enable = true; }; }', is
  rejected, which is kind of ugly.)

tests/lang/eval-okay-context.exp

@@ -1 +1 @@
-Str("foo eval-okay-context.nix bar",[])
+"foo eval-okay-context.nix bar"

tests/lang/parse-fail-dup-attrs-7.nix

@@ -0,0 +1,9 @@
+rec {
+
+  x = 1;
+
+  as = {
+    inherit x;
+    inherit x;
+  };
+}