code review request: 6894072: always refresh keytab

[Weijun Wang]

Hi Valerie

Updated webrev:

    http://cr.openjdk.java.net/~weijun/6894072/webrev.02

Changes since last version:

1. A KerberosPrincipal inside javax..KeyTab class. New getInstance() 
arguments, new getPrincipal() method.

It can only be non-null now, but I didn't say anything in the spec. I'm 
hoping it can be null in the future to support multiple service 
principal in a single service.

2. toString(), hashCode(), equals() for KeyTab, since it will be put 
inside private credentials set.

3. Enhancement to SubjectComber:
    a) Generics for find() and findMany()
    b) findAux() now support Krb5AcceptCredential

4. Krb5Util.ServiceCreds: since principal is already inside both KeyTab 
and KerberosKey, no more KerberosPrincipal argument in getInstance(), 
there is still a field inside to save the value.

5. sun..KeyTab and javax..KeyTab: isMissing==true is now valid. Changes 
to the javadoc of javax..KeyTab.getKeys().

6. New TwoPrinces.java test, a subject with 2 KerberosPrincipal after 
JAAS commit.

This time I'd like to first make sure implementation is correct, and 
then I'll update the CCC. Is this OK?

Thanks
Max