(v5_to_kt): new function, stores a krb5_creds in struct kafs_token
(get_cred): add a appdefault boolean ("libkafs", realm, "afs-use-524")
that can used to toggle if there should v5 token should be used
directly or converted via 524 first.
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@11837 ec53bebd-3082-4978-b11e-865c3cabbd6b