AD DNS and Global sequence number implementation

[Andrew Tridgell]

Hi Amitay,

This is great work, thanks! 

> To overcome this problem, I have put together few patches that use a
> TDB database (metadata.tdb) to store the sequence number. This way the
> sequence number is independent of the partitions and survives deletion
> of partitions.

I should also mention for the benefit of others following this thread
that we need this change even without the bind9 work, as without it we
will have a lot of trouble when we start supporting deleting
partitions. We need to be able to delete application partitions, and
also remove partitions associated with subdomains if the admin says we
should no longer be replicating those partitions.

The method of using the sum of the partition sequence numbers as the
overall SAM sequence number is just too fragile, and it's good for us to
have this new approach.

Cheers, Tridge