s4: fsmo role transfer

[tridge at samba.org]

Hi Nadya,

Andrew and I looked over your FSMO role transfer patches today. Very
nice work! You are producing some great code.

Andrew spotted one thing, which is that the rootdse role transfers
don't seem to be protected by any authentication or ACL. Maybe we
could just have a simple security level check on these changes in the
rootdse code?  Alternatively you could send the token in the irpc call
to the drepl server and have it do authentication or ACL checks.

The simplest is probably to say that rootdse modify is denied unless
you are at least SECURITY_DOMAIN_CONTROLLER level.

We also fixed up some build breakages caused by some recent changes in
the drepl server, and the conversion of the IRPC code to use binding
handles. We've put a fixed and rebased copy of your fsmo-fixed branch
in the nadya-fsmo-fixed in my git tree.

Cheers, Tridge