Raise a warning when listen = hostname used and is resolved as multiple addresses

Using getaddrinfo is perhaps not a good idea... if we are not able
to listen on multiple addresses...

At least this message should help to diagnose problem, ex
... Found address for localhost, socket opened on ::1
... Found multiple addresses for localhost, 127.0.0.1 ignored
Fix bug #68463 listen.allowed_clients can silently result in no allowed access

Add a "There are no allowed addresses for this pool"
NEWS