new interfaces code (bug fix + questions)

[tridge at linuxcare.com]

> Again, hard to tell. Immediate con is the case of compiling on a
> system without network :-) Is probably rare. The worst case is a
> system, that supports both, but returns less intefaces with IFCONF
> (sockets) than with IFREQ (STREAMS TLI).

if such a system turns up then we can look at it. Right now the code
works on all systems that we have access to so I'll probably leave it
and wait for someone to complain. 

Note that if it does get it wrong users can still use an interfaces=
line to override it all.

Cheers, Tridge