anchor.diff: -{ fetchurl, stdenv, fixDarwinDylibNames
  +{ fetchurl, stdenv
   , pkgconfig, gnupg
   , xapian, gmime, talloc, zlib
   , doxygen, perl
  
positive.code:       substituteInPlace "$src" \
          --replace \"gpg\" \"${gnupg}/bin/gpg\"
      done
    '';
  
    configureFlags = [ "--zshcompletiondir=$(out)/share/zsh/site-functions" ];
  
negative.code:     bash-completion  # (optional) dependency to install bash completion
      emacs  # (optional) to byte compile emacs code, also needed for tests
      ruby  # (optional) ruby bindings
    ];
  
    postPatch = ''
      patchShebangs configure
      patchShebangs test/
  
      for src in \
        util/crypto.c \
  