Eliminate domain-based client realm walk

Eliminate domain-based client realm walk

For a very long time, KDCs have known how to perform a domain-based
realm walk when serving requests for TGTs.  (So if a KDC for A.B.C
receives a request for krbtgt/X.B.C and doesn't have that principal,
it can return one for krbtgt/B.C instead.)  Performing the same
heuristic on the client is unnecessary and inefficient in common
cases.

Add a new function k5_client_realm_path to walk_rtree.c which uses
capaths values only, and returns a list of realms (as desired by
get_creds.c) instead of TGT names.

ticket: 6966

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25241 dc483132-0cff-0310-8789-dd5450dbe970