Incomplete D7 port: uniqueness_content_extra_fields needs to become uniqueness_field_extra_fields

Port of hook_content/field_extra_fields ready for review.

/**
 * Implements hook_field_extra_fields().
 *
 * Allows the inline uniqueness field to be sorted on the manage fields page for
 * any content type for which it is enabled.
 */
function uniqueness_field_extra_fields() {
  $extras = array();
  if (in_array(UNIQUENESS_WIDGET_INLINE, variable_get('uniqueness_widgets', array(UNIQUENESS_WIDGET_INLINE)))) {
    // The inline widget is enabled
    foreach (array_keys(node_type_get_types()) as $type) {
      $v = variable_get('uniqueness_type_' . $type, array());
      if (!empty($v)) {
        $extras['node'][$type] = array(
          'form' => array(
            'uniqueness' => array(
              'label' => filter_xss_admin(variable_get('uniqueness_default_title', t('Related content'))),
              'description' => t('Uniqueness inline widget.'),
              'weight' => 0,
            ),
          ),
        );
      }
    }
  }

  return $extras;
}