Map MailChimp input to Drupal FormAPI (patch attached)

Hi all,

Here is a small patch that maps Dropdown et Radios from MailChimp to Drupal FormAPI. With that newsletter subscription form displays nice widgets.

i.e. : no more textfield input when telling MailChimp form builder to render a dropdown.

I also added a test condition so that hidden fields (from MailChimp) renders hidden fields in Drupal.

Unfortunaltely, the MailChimp date input can't be supported easily for now.

Last, I just made a small modification to form validate, which was letting me subscribe to a newsletter even if I did not checked the box (the small '1' added).

Look at the patch.

Thank you guys!
Jérémy