r10561: This patch takes over KDC socket routines in Heimdal, and directs them

r10561: This patch takes over KDC socket routines in Heimdal, and directs them
at the Samba4 socket layer.

The intention here is to ensure that other events may be processed while
heimdal is waiting on the KDC.  The interface is designed to be
sufficiently flexible, so that the plugin may choose how to time
communication with the KDC (ie multiple outstanding requests, looking
for a functional KDC).

I've hacked the socket layer out of cldap.c to handle this very
specific case of one udp packet and reply.  Likewise I also handle
TCP, stolen from the winbind code.

This same plugin system might also be useful for a self-contained
testing mode in Heimdal, in conjunction with libkdc.  I would suggest
using socket-wrapper instead however.

Andrew Bartlett