static ItIt<File> filesContainingText(S text, Iterable<File> l) {
  byte[] bytes = toUtf8(text);
  ret filterI(iterator(l), f -> fileContainsBytes(f, bytes));
}

static ItIt<File> filesContainingText(Iterable<File> l, S text) {
  ret filesContainingText(text, l);
}