Add copyright notices.

servers/slapd/abandon.c

servers/slapd/acl.c

servers/slapd/aclparse.c

servers/slapd/add.c

servers/slapd/attr.c

servers/slapd/ava.c

servers/slapd/back-ldbm/abandon.c

servers/slapd/back-ldbm/add.c

servers/slapd/back-ldbm/attr.c

servers/slapd/back-ldbm/back-ldbm.h

servers/slapd/back-ldbm/bind.c

servers/slapd/back-ldbm/cache.c

servers/slapd/back-ldbm/close.c

servers/slapd/back-ldbm/compare.c

servers/slapd/back-ldbm/config.c

servers/slapd/back-ldbm/dbcache.c

servers/slapd/back-ldbm/delete.c

servers/slapd/back-ldbm/dn2id.c

servers/slapd/back-ldbm/entry.c

servers/slapd/back-ldbm/external.h