Mainly BDC-related changes.

Mainly BDC-related changes.

* Added SEC_CHAN_BDC
* Propagate sec_chan into the various functions which change trust account
  passwords, so they can be used for domain control and inter-domain
  trusts.
* Fix for endianness problem reported by Edan Idzerda <edan@mtu.edu>. A
  BUFFER2 is really a "unibuf" in my terminology and we should treat it as
  such.
* Added some more common NT structures (BIGINT, BUFHDR2, BUFFER4).
* Added NET_SAM_SYNC (-> NetDatabaseSync2) RPC for account replication.
  Still experimental and incomplete, with a few too many NULL security
  descriptors lying around (must go look at Jeremy's SD code). Haven't
  worked out password encryption yet either.
  However, the XXX_INFO structures I've added to rpc_netlogon.h are quite
  nice as they give some insight into how these objects are stored in the
  SAM.
(This used to be commit 7b830350eb54dc9d357c115e12ddf9a0633527ac)