Add copyright notice and a few comments here and there

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

servers/slapd/back-ldbm/external.h

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

servers/slapd/daemon.c

servers/slapd/main.c

servers/slapd/proto-slap.h

servers/slapd/slap.h

servers/slapd/tools/ldbmcat.c

servers/slapd/tools/ldbmtest.c

servers/slapd/tools/ldif.c

servers/slapd/tools/ldif2id2children.c

servers/slapd/tools/ldif2id2entry.c

servers/slapd/tools/ldif2index.c

servers/slapd/tools/ldif2ldbm.c

servers/slapd/tools/mimic.c