RFR 8071643: sun.security.krb5.KrbApReq.authenticate() is not thread safe

[Weijun Wang]

Hi All

Please review the code change at

   http://cr.openjdk.java.net/~weijun/8071643/webrev.00/

The static field is removed and a local MessageDigest is used. The 
getInstance() method might spend some time but since there are already 
quite some cipher and checksum operations during an AP-REQ receive, this 
change does not make much difference.

No reg, could be -hard and -trivial.

Thanks
Max