r7294: implemented the irpc messaging system. This is the core of the

r7294: implemented the irpc messaging system. This is the core of the
management system I proposed on samba-technical a couple of days
ago. Essentially it is a very lightweight way for any code in Samba to
make IDL based rpc calls to anywhere else in the code, without the
client or server having to go to the trouble of setting up a full rpc
service.

It can be used with any of our existing IDL, but I expect it will
mostly be used for a new set of Samba specific management calls.

The LOCAL-IRPC torture test demonstrates how it can be used by calling
the echo_AddOne() call over this transport.