Shopify/active_merchant — pull request #440 by duff (2012-08-21 18:39:22+00:00)
Title: Add refund method to Viaklix gateway.

This brings Viaklix and Elavon in line with the other gateways in that
the #credit method is deprecated and the refund method is the
recommended path.

Viaklix and Elavon are a bit unconventional in that they don't seem to
support credit via reference. Instead, they require the full card
details again to do a credit. In fact, they seem to require the card to
do a capture as well.

All in all, it's sub-optimal, but at least things are now a little more
consistent with the other direct gateways.