Allow for export of user D7 entity fields to slave sites

Bakery's configuration form does not currently include fields added to the user entity in Drupal 7. The current code in bakery.module includes a legacy snippet that was intended to work with Drupal 6's profile project, and added those custom fields to the form. See lines 614-619:

  if (module_exists('profile')) {
    $result = db_query('SELECT name, title FROM {profile_field} ORDER BY category, weight');
    foreach ($result as $field) {
      $options[$field->name] = check_plain($field->title);
    }
  }

This obviously will not work in Drupal 7.