gnupdate: Really select `stdenv' packages when asked for it.

* maintainers/scripts/gnu/gnupdate (gnupdate)[selected-gnu-packages]:
Really limit to `stdenv' when ask for it.

svn path=/nixpkgs/trunk/; revision=30869

maintainers/scripts/gnu/gnupdate

···
 
     (case selection
       ((stdenv)
-       gnu)
+       (filter (lambda (p)
+                 (member (package-source-output-path p)
+                         (force stdenv)))
+               gnu))
       ((non-stdenv)
        (filter (lambda (p)
                  (not (member (package-source-output-path p)