Configure MessagePack to be a bit more like gob

By default codec's MessagePack encode/decode will convert a string
into a []byte.  Tweak the settings so that string -> string and []byte
-> []byte.

packer/rpc/client.go

@@ -40,8 +40,11 @@ func newClientWithMux(mux *muxBroker, streamId uint32) (*Client, error) {
 		return nil, err
 	}
 
-	var h codec.MsgpackHandle
-	clientCodec := codec.GoRpc.ClientCodec(clientConn, &h)
+	h := &codec.MsgpackHandle{
+		RawToString: true,
+		WriteExt:    true,
+	}
+	clientCodec := codec.GoRpc.ClientCodec(clientConn, h)
 
 	return &Client{
 		mux:      mux,

packer/rpc/server.go

@@ -148,8 +148,11 @@ func (s *Server) Serve() {
 	}
 	defer stream.Close()
 
-	var h codec.MsgpackHandle
-	rpcCodec := codec.GoRpc.ServerCodec(stream, &h)
+	h := &codec.MsgpackHandle{
+		RawToString: true,
+		WriteExt:    true,
+	}
+	rpcCodec := codec.GoRpc.ServerCodec(stream, h)
 	s.server.ServeCodec(rpcCodec)
 }