Singletons / multiple requests bug

[fsalomon]

Why are you using singletons for stuff like CheckoutApi_Lib_RespondObj and CheckoutApi_Lib_ExceptionState? Seems like a poor design decision.

This is causing a critial bug: If one request fails and throws an exception, subsequent requests will throw exceptions, too. That's because CheckoutApi_Lib_ExceptionState is reused. To reproduce, make one verifyPaymentToken request with an invalid token and then try doing a createPaymentToken request. Both requests will throw an exception.