net/rpc: document that Register logs to standard error

Also fix spurious & in example.

Fixes #4349.
Fixes #4489.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/6905058

src/pkg/net/rpc/server.go

@@ -112,7 +112,7 @@
 
 		// Asynchronous call
 		quotient := new(Quotient)
-		divCall := client.Go("Arith.Divide", args, &quotient, nil)
+		divCall := client.Go("Arith.Divide", args, quotient, nil)
 		replyCall := <-divCall.Done	// will be equal to divCall
 		// check errors, print, etc.
 
@@ -219,8 +219,8 @@ func isExportedOrBuiltinType(t reflect.Type) bool {
 //	- exported method
 //	- two arguments, both pointers to exported structs
 //	- one return value, of type error
-// It returns an error if the receiver is not an exported type or has no
-// suitable methods.
+// It returns an error if the receiver is not an exported type or has
+// no methods or unsuitable methods. It also logs the error using package log.
 // The client accesses each method using a string of the form "Type.Method",
 // where Type is the receiver's concrete type.
 func (server *Server) Register(rcvr interface{}) error {