Built-in resolver hides DNS errors

[yary]

I was trying to test out notification by putting in the config file a
group I knew would fail:

Host "Fail.notopdomain.xyz" {
  Service Ping
}

... and yet, Fail.notopdomain.xyz always came up "green", regardless
of the services I tried.

After commenting out the built-in resolver "Resolv", Argus
appropriately complains "Errors detected during startup", and
highlights the error log.

The built-in resolver should also complain if it can't resolve a hostname!