nixos.org/tarballs. It no longer greps the source for fetchurl
calls, because a lot of URLs are now computed
(e.g. "http://foo/${name}.tar.bz2"). So instead we evaluate the Nix
expression with "nix-instantiate --xml --strict" and look for URLs
in the result. Because I'm lazy the script no longer checks whether
the hash of the download matches the hash in the expression.
svn path=/nixpkgs/trunk/; revision=15310
