anchor.diff:  
   let
     # if you bump version, update pkgs.tortoisehg too or ping maintainer
  -  version = "3.7.3";
  +  version = "3.8.1";
     name = "mercurial-${version}";
   in
   
  
positive.code: 
    src = fetchurl {
      url = "http://mercurial.selenic.com/release/${name}.tar.gz";
      sha256 = "0c2vkad9piqkggyk8y310rf619qgdfcwswnk3nv21mg2fhnw96f0";
    };
  
    inherit python; # pass it so that the same version can be used in hg2git
  
negative.code:     downloadPage = "http://mercurial.selenic.com/release/";
      license = stdenv.lib.licenses.gpl2;
      maintainers = [ stdenv.lib.maintainers.eelco ];
      updateWalker = true;
    };
  }
  