Jersey Client DigestAuthenticator: qop=auth-int support added

Hi, 
I recently needed the integrity check mechanism for Digest Auth, so I implemented it. Now both auth and auth-int are supported.
I also added a few more test cases.
Please review. I am not 100% sure whether my method for looking up the MessageBodyWriter in DigestAuthenticator.java is the most optimal solution possible.
Stefan Katerkamp