ntdb: special accessor functions for read/write of an offset.

ntdb: special accessor functions for read/write of an offset.

We also split off the NTDB_CONVERT case (where the ntdb is of a
different endian) into its own io function.

NTDB speed:
Adding 10000 records: 3894-9951(8553) ns (815528 bytes)
Finding 10000 records: 1644-4294(3580) ns (815528 bytes)
Missing 10000 records: 1497-4018(3303) ns (815528 bytes)
Traversing 10000 records: 1585-4225(3505) ns (815528 bytes)
Deleting 10000 records: 3088-8154(6927) ns (815528 bytes)
Re-adding 10000 records: 3192-8308(7089) ns (815528 bytes)
Appending 10000 records: 5187-13307(11365) ns (1274312 bytes)
Churning 10000 records: 6772-17567(15078) ns (1274312 bytes)
NTDB speed in transaction:
Adding 10000 records: 1602-2404(2214) ns (815528 bytes)
Finding 10000 records: 456-871(778) ns (815528 bytes)
Missing 10000 records: 393-522(503) ns (815528 bytes)
Traversing 10000 records: 729-1015(945) ns (815528 bytes)
Deleting 10000 records: 1065-1476(1374) ns (815528 bytes)
Re-adding 10000 records: 1397-1930(1819) ns (815528 bytes)
Appending 10000 records: 2927-3351(3184) ns (1274312 bytes)
Churning 10000 records: 3921-4697(4378) ns (1274312 bytes)
smbtorture results:
ntdb speed 86581-191518(175666) ops/sec
Applying patch..increase-top-level.patch