protected function mungeExcludeLists($file1, $file2) {
    $file1_contents = file($file1);
    $file2_contents = file($file2);
    $merged = array_merge($file1_contents, $file2_contents);
    $merged_without_dups = array_unique($merged);
    file_put_contents($this->excludeFileTemp, $merged_without_dups);

    return $this->excludeFileTemp;
  }