Use port number 0 for ephemeral port

Hopefully RFC-6056 is being applied.
Fixes #63.

Author: nobu

lib/resolv.rb

@@ -660,14 +660,8 @@ def self.free_request_id(host, port, id) # :nodoc:
     end
 
     def self.bind_random_port(udpsock, bind_host="0.0.0.0") # :nodoc:
-      begin
-        port = random(1024..65535)
-        udpsock.bind(bind_host, port)
-      rescue Errno::EADDRINUSE, # POSIX
-             Errno::EACCES, # SunOS: See PRIV_SYS_NFS in privileges(5)
-             Errno::EPERM # FreeBSD: security.mac.portacl.port_high is configurable.  See mac_portacl(4).
-        retry
-      end
+      # Simply use 0 with assuming RFC-6056 is applied.
+      udpsock.bind(bind_host, 0)
     end
 
     class Requester # :nodoc: