Refund reason

Some payment gateways accept a reason string that is viewable within their portal/dashboard etc. This change passes the refund reason to the gateway's process_refund() method allowing them to use it if required.

Other gateways would need updating, as would the post here if this is accepted:

http://develop.woothemes.com/woocommerce/2014/08/wc-2-2-payment-gateways-adding-refund-support-and-transaction-ids/?utm_source=rss&utm_medium=rss&utm_campaign=wc-2-2-payment-gateways-adding-refund-support-and-transaction-ids