anchor.diff:  { stdenv, fetchurl
   , bzip2
  -, db
   , gdbm
   , libX11, xproto
   , lzma
  
positive.code:     lzma
      gdbm
      sqlite
      db
      readline
      ncurses
      openssl
  
negative.code:   passthru = rec {
      zlibSupport = zlib != null;
      sqliteSupport = sqlite != null;
      dbSupport = false;
      readlineSupport = readline != null;
      opensslSupport = openssl != null;
      tkSupport = (tk != null) && (tcl != null) && (libX11 != null) && (xproto != null);
  