redesign of back-bdb locking :

servers/slapd/back-bdb/add.c

servers/slapd/back-bdb/attribute.c

servers/slapd/back-bdb/back-bdb.h

servers/slapd/back-bdb/bind.c

servers/slapd/back-bdb/cache.c

servers/slapd/back-bdb/compare.c

servers/slapd/back-bdb/delete.c

servers/slapd/back-bdb/dn2entry.c

servers/slapd/back-bdb/group.c

servers/slapd/back-bdb/id2entry.c

servers/slapd/back-bdb/modify.c

servers/slapd/back-bdb/modrdn.c

servers/slapd/back-bdb/operational.c

servers/slapd/back-bdb/passwd.c

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

servers/slapd/back-bdb/referral.c

servers/slapd/back-bdb/search.c