Make credit card not required for 100% discount

Created by: joshfttb

Current setup works well with the Paypal Standard payment processor. However, processors that require credit card info on page (such as Stripe) cannot be submitted without CC info, even if the discount is 100%. Most people with 100% discounts will not want to enter their credit card information. These field should not be required (and possibly hidden) when the discount is 100%. Some possible approaches are described here: http://drupal.org/node/1140220