resolvconf prefers a locally running BIND resolver over the forwarders; we just
have to tell it whether we have one or not. We use 'config.services.bind.enable'
to make that decision, assuming that people are not going to configure a local
BIND that won't respond to queries on 127.0.0.1. If we run into such a (weird)
case, then we'll need to introduce another variable for that purpose which can
be set independently from 'config.services.bind.enable'.
This change allows using extraHosts to specify additional aliases for 127.0.0.1
without overriding the local hostname in the process.
svn path=/nixos/trunk/; revision=32711
