p2p: use package rlp to encode messages

Message encoding functions have been renamed to catch any uses.
The switch to the new encoder can cause subtle incompatibilities.
If there are any users outside of our tree, they will at least be
alerted that there was a change.

NewMsg no longer exists. The replacements for EncodeMsg are called
Send and SendItems.

p2p/peer.go

@@ -132,7 +132,7 @@ loop:
 		select {
 		case <-ping.C:
 			go func() {
-				if err := EncodeMsg(p.rw, pingMsg, nil); err != nil {
+				if err := SendItems(p.rw, pingMsg); err != nil {
 					p.protoErr <- err
 					return
 				}
@@ -161,7 +161,7 @@ loop:
 func (p *Peer) politeDisconnect(reason DiscReason) {
 	done := make(chan struct{})
 	go func() {
-		EncodeMsg(p.rw, discMsg, uint(reason))
+		SendItems(p.rw, discMsg, uint(reason))
 		// Wait for the other side to close the connection.
 		// Discard any data that they send until then.
 		io.Copy(ioutil.Discard, p.conn)
@@ -192,7 +192,7 @@ func (p *Peer) handle(msg Msg) error {
 	switch {
 	case msg.Code == pingMsg:
 		msg.Discard()
-		go EncodeMsg(p.rw, pongMsg)
+		go SendItems(p.rw, pongMsg)
 	case msg.Code == discMsg:
 		var reason [1]DiscReason
 		// no need to discard or for error checking, we'll close the