Merge from HEAD - save the type of channel used to contact the DC.

Merge from HEAD - save the type of channel used to contact the DC.

This allows us to join as a BDC, without appearing on the network as one
until we have the database replicated, and the admin changes the configuration.

This also change the SID retreval order from secrets.tdb, so we no longer
require a 'net rpc getsid' - the sid fetch during the domain join is sufficient.
Also minor fixes to 'net'.

Andrew Bartlett