missing options_validate() for views display plugin

Cribbed from Party:

    // Only allow word characters and hyphens.
    // TODO: make this match accented characters.
    if (preg_match('/[^\w-]/', $form_state['values']['party_piece_path'])) {
      form_error($form['party_piece_path'], t('The path may only contain letters, numbers, underscores, and hyphens.'));
    }

    // Check for duplicate paths.
    $pieces = party_get_party_piece_info();
    if (isset($pieces[$form_state['values']['party_piece_path']])) {
      form_error($form['party_piece_path'], t('The path already exists.'));
    }

We probably don't want the duplicate paths validation, as we intentionally allow Views displays to override hardcoded operation paths. But we definitely need the first.