Updated verify() method for verifying PayPal IPN Messages

- Fixed from r1133 https://code.google.com/p/fluxcp/source/detail?r=1133
- Should fix issues related to
http://hercules.ws/board/topic/1901-flux-control-panel-for-hercules/?p=3
0478 and
http://hercules.ws/board/topic/4661-need-support-regarding-paypal-config
uration/