title: Add an auto_increment column in Magento setup script without using SQL
body: <p>Previously I asked how to <a href="https://stackoverflow.com/q/4315660/471559">ALTER TABLE in Magento setup script without using SQL</a>. There, <a href="https://stackoverflow.com/users/465971/ivan-chepurnyi">Ivan</a> gave an excellent answer which I still refer to even now.</p>
  
  <p>However I have yet to discover how to use <code>Varien_Db_Ddl_Table::addColumn()</code> to specify an <code>auto_increment</code> column. I think it has something to do with an option called <code>identity</code> but so far have had no luck.</p>
  
  <p>Is this even possible or is that functionality incomplete?</p>