Create D5 -> D6 upgrade path

This should get you started. I thought I'd finish it out, but then it occurred to me that renaming mailkey to id might not be the right thing to do since mailkey is in the new registry table. Since I don't have any data in my table yet, I don't know what data if any needs to move between the tables in an upgrade.

function mail_edit_update_6000() {
  $ret = array();
  db_drop_primary_key($ret, 'mail_edit');
  db_add_field($ret, 'mail_edit', 'language', array(
      'type' => 'varchar',
      'length' => '10',
      'not null' => TRUE,
      'description' => t(''),
    )
  );
  db_change_field($ret, 'mail_edit', 'mailkey', 'id', array(
      'type' => 'varchar',
      'length' => '255',
      'not null' => TRUE,
      'description' => t(''),
    )
  );
  db_add_index($ret, 'mail_edit', '`unique entry`', array('`id`', '`language`'));
  db_add_index($ret, 'mail_edit', '`id`', array('`id`'));
  db_add_index($ret, 'mail_edit', '`language`', array('`language`'));

  db_create_table($ret, 'mail_edit_registry', array(
      'description' => t(''),
      'fields' => array(
        'id' => array(
          'type' => 'varchar',
          'length' => '255',
          'not null' => TRUE,
          'description' => t(''),
        ),
        'module' => array(
          'type' => 'varchar',
          'length' => '255',
          'not null' => TRUE,
          'description' => t(''),
        ),
        'mailkey' => array(
          'type' => 'varchar',
          'length' => '255',
          'not null' => TRUE,
          'description' => t(''),
        ),
        'description' => array(
          'type' => 'varchar',
          'length' => '255',
          'not null' => TRUE,
          'description' => t(''),
        ),
      ),
      'primary key' => array('`id`')
    )
  );
  return $ret;
}