title: Wordpress Mailchimp Form custom checkbox
body: <p>I'm using the <a href="http://wordpress.org/extend/plugins/mailchimp/" rel="nofollow">Mailchimp subscription plugin</a> for wordpress (v. 1.2.13). It's all ok, I just need to add a checkbox to accept privacy terms. I've created that field through the <a href="http://kb.mailchimp.com/article/advanced-customization-of-mailchimps-sign-up-forms" rel="nofollow">Mailchimp form managment</a>, it shows and works in the form except that <strong>I need to define it as required</strong>. There is no option for that in mailchimp, i tried to add a simple "required" attribute in html, but it didn't work (as expected). </p>
  
  <p>Any suggestion?</p>
  
  <p>I've also spotted that Mailchimp define if that field is required in an array/place called <code>$var['req']</code> that is someway connected with the field name. But I can't find where can I access this array or how to add my custom field to that.</p>