Major improvements in the security of the CAPTCHA system (no SQL injection or anything like that); fixed denied form submission due to _af_acting on form object wrongly switched to true

<?php

class Text_Wiki_Render_Plain extends Text_Wiki_Render {
    
    function pre()
    {
        return;
    }
    
    function post()
    {
        return;
    }
    
}
?>