Difference between hook_schema() and simplenews_update_6254()

Hi,

In simplenews_update_6254(), we can find

 db_add_field($ret, 'simplenews_mail_spool', 'snid', array(                                                                                                 
    'description' => 'Foreign key for subscriber table ({simplenews_subscriptions}.snid)',
    'type' => 'int',
    'unsigned' => TRUE,
    'not null' => TRUE,
    'default' => 0,
  ));

whereas in hook_schema() there is no 'default' => 0 (neither in Drupal 7 hook_schema()).

These patchs add the 'default' => 0 to both 6.x-2.x and 7.x versions.