Fix #710

When using http proxy, this will cause distinct latency
if we are trying to resolve localhost.

Currently it's unnecessary to do that because our privoxy
doesn't listern on ipv6 address, so it's ok to hard code
the ipv4 address.

There is a plan to add a cache to record the ipv6 connectivity
so that we needn't to try both ipv4 and ipv6 every time when we
attempt to connect a DnsEndPoint.

shadowsocks-csharp/Controller/Service/PortForwarder.cs

@@ -46,7 +46,7 @@ namespace Shadowsocks.Controller
                 this._local = socket;
                 try
                 {
-                    EndPoint remoteEP = SocketUtil.GetEndPoint("localhost", targetPort);
+                    EndPoint remoteEP = SocketUtil.GetEndPoint("127.0.0.1", targetPort);
 
                     // Connect to the remote endpoint.
                     _remote = new WrappedSocket();