(dns_resolution): Schedule an idle check, as a client may have
	become unblocked.  Don't call isc_enable() here.  Instead, add
	the session to the run-queue.  There may be pending input in
	the input buffer.  Handle ADNS errors.
(login_request): Check the return value of isc_resolve_remote().
(read_from_connection): Return if the session is blocked by DNS.