Add tests for AbstractRequest
Add tests for AbstractResponse
Clean up AbstractResponse::getRedirectResponse
Fix ignored test case

Was ignored because filename did not end in *Test.php. Also
requied a few updates to keep pace with current state of codebase.
Add tests for PayPal CaptureRequest
Add tests for ExpressCompleteAuthorizeRequest
Add tests for PayPal RefundRequest
Add tests for PayPal ExpressAuthorizeRequest
Add tests for PayPal ExpressAuthorizeResponse
Add tests for Netaxept PurchaseRequest
Add tests for Netaxept PurchaseRequest
Add tests for Netaxept CompletePurchaseRequest