custom allocation.

* certificate.c (spki_realloc): Deleted function.
(spki_acl_init): Use nettle_realloc.
(acl_by_auth): Take a struct spki_tag argument.
(spki_acl_by_authorization_next): Likewise.
(spki_acl_by_authorization_first): Likewise.
(spki_5_tuple_free_chain): Use spki_tag_release.

Rev: src/spki/certificate.c:1.16
Rev: src/spki/certificate.h:1.15