child_process: allow sending a net Socket and Server object using child.send

child_process.fork() support sending native hander object, this patch add support for sending
net.Server and net.Socket object by converting the object to a native handle object and back
to a useful object again.

Note when sending a Socket there was emitted by a net Server object, the server.connections
property becomes null, because it is no longer possible to known when it is destroyed.