OPEN - task 26: Logging leaks sensitive information 
https://github.com/paypal/sdk-core-java/issues/issue/26

Changed filtering of payload to encompass Username, Password, Signature,
Subject, CreditCardNumber, and CVV2.

This should help to prevent leakage of this information into log files
which are, shall we say, frowned upon by PCI and FFIEC auditors.
Committed recommended changes from @juwon
Merge pull request #27 from djgraff209/logging-pci-leak

Logging leaks sensitive information