Add support for referral null realms and use the default realm as krb5_rd_req_extended does

https://github.com/krb5/krb5/commit/868264bf7c324b16d275493bcc3438125f9b1680
Commit By: hartmans
Revision: 21716
Changed Files:
U   trunk/src/lib/krb5/krb/vfy_increds.c