static LS flite_listVoices() {
  if (!flite_installed()) ret emptyList();
  new TreeSet<S> set;
  set.addAll(splitAtSpace(getColonProperty("Voices available", lines(backtick("flite -lv")))));
  new Matches m;
  for (File dir : flite_voiceDirs())
    for (S s : listFileNames(dir))
      if (endsWith(s, ".flitevox", m))
        set.add(m.rest());
  ret asList(set);
}