anchor.diff:  
     src = fetchurl {
       url = "http://mercurial.selenic.com/release/${name}.tar.gz";
  -    sha256 = "0c2vkad9piqkggyk8y310rf619qgdfcwswnk3nv21mg2fhnw96f0";
  +    sha256 = "156m6269xdqq7mpw01c6b065k29xnb8b9lyzn1b0nlz5il2izkps";
     };
   
     inherit python; # pass it so that the same version can be used in hg2git
  
positive.code:     downloadPage = "http://mercurial.selenic.com/release/";
      license = stdenv.lib.licenses.gpl2;
      maintainers = [ stdenv.lib.maintainers.eelco ];
    };
  }
  
negative.code: 
  let
    # if you bump version, update pkgs.tortoisehg too or ping maintainer
    version = "3.8.1";
    name = "mercurial-${version}";
  in
  
  