Shopify/active_merchant — pull request #1303 by duff (2014-07-12 17:19:00+00:00)
Title: BraintreeBlue: Remember the capture transaction id

Now the response from a capture actually has a value for its
authorization. This allows captures to be voided before they're settled
and refunded after that.

I'm surprised this hasn't been hit before. Without it, it's difficult
to refund/void captures.