xC/xP: send buffer input history during sync

This transfer is currenly quite simplistic,
but it paves the way for further extensions.

xP/public/xP.js

@@ -387,6 +387,15 @@ rpcEventHandlers.set(Relay.Event.BufferActivate, e => {
 	}
 })
 
+rpcEventHandlers.set(Relay.Event.BufferInput, e => {
+	let b = buffers.get(e.bufferName)
+	if (b === undefined)
+		return
+	if (b.historyAt == b.history.length)
+		b.historyAt++
+	b.history.push(e.text)
+})
+
 rpcEventHandlers.set(Relay.Event.BufferClear, e => {
 	let b = buffers.get(e.bufferName)
 	if (b !== undefined)