Reimplement LDBM_SYNC/LDBM_NOSYNC code (dbnosync).
Old code applied sync flags to store(), however supported DBMs require such flags to be specified during open(). The new code now applies flags in ldbm_cache_open (which calls ldbm_open). ldbm_cache_close() now calls ldbm_sync(). This will force a updating of on-disk contents after each LDAP operation. The old code either failed to sync the on-disk contents until close or synced on every store. Per LDBM operation syncing *should* be safe enough... real data safety requires transactions. Removed nosync option from BDB2 as it is not compatible with txn support. Also added code to disable DBM level locking as slapd is only process acessing the databases (dbnolocking).