* More work on config error messages + some code restructure to trap config

*  More work on config error messages + some code restructure to trap config
   errors better.

*  Fixed bug in 'implicit loopback'

*  Completely removed duplicate interface usage checks from generic network
   setup.  The NAL should be doing this.   Currently socknal is the only one
   that supports multiple instances and it doesn't mind at all if 2 different
   network instances use the same interfaces, and that's dead useful for
   testing.

*  Tightened up lonal refcounting; there was a remote chance of a shutdown
   race.