As per #734, this restores the original void behaviour to work on captures and purchases and combines the update in d9a10567587efb6652aece2da9a74ec7be007711 to allow the cancellation of an authorization by passing `:authorization => true` as an option whe

(Note that the Moneris test gateway is flakey. Under normal circumstances, all tests pass; but when the gateway is flakey, there may be failures which appear to be caused by invalid XML.)