Document new FAPI property, #limit_validation_errors

#370537: Allow suppress of form errors (hack to make "more" buttons work properly) introduced a new FAPI property, #limit_validation_errors, that can be applied to buttons, image buttons, and submit types. I'm not sure whether this needs to be mentioned in http://drupal.org/update/modules/6/7. But it definitely needs to be added to http://api.drupal.org/api/drupal/developer--topics--forms_api_reference.....

Poll module's poll_form() function has an example. In D6, to add a choice, you needed to have the required "Question" field filled in. In D7, with this property, you don't need the "Question" field filled in to add a choice.

More detailed documentation currently exists in the documentation for parameters to form_set_error().