The GSS mechglue uses singly linked lists for mechanisms and mechanism objects,
to which new entries are inserted at the head. This breaks ordering of
mechanisms specified in OID sets and in /etc/gss/mech, as they will be back to
front. Use a tail queue instead so that new entries are inserted at the end.
Implementation of gss_set_neg_mechs() and gss_get_neg_mechs() as defined in RFC
4178. New gss_release_cred_by_mech() API for dropping a credential from a
mechanism glue credential.