gss_store_cred_into*() will now switch the new cred cache to be the
primary/default cred cache when
- the caller requested it and,
- if the caller passed in a user name, the creds' principal is the best
principal for the named user.
A principal is the best principal for a user when the principal has just
one component, the component is the user's username, and the realm is
the configured user_realm.