bytes: make examples work in playground

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6633050

src/pkg/bytes/example_test.go

@@ -5,23 +5,24 @@
 package bytes_test
 
 import (
-	. "bytes"
+	"bytes"
 	"encoding/base64"
+	"fmt"
 	"io"
 	"os"
 )
 
 func ExampleBuffer() {
-	var b Buffer // A Buffer needs no initialization.
+	var b bytes.Buffer // A Buffer needs no initialization.
 	b.Write([]byte("Hello "))
-	b.Write([]byte("world!"))
+	fmt.Fprintf(&b, "world!")
 	b.WriteTo(os.Stdout)
 	// Output: Hello world!
 }
 
 func ExampleBuffer_reader() {
 	// A Buffer can turn a string or a []byte into an io.Reader.
-	buf := NewBufferString("R29waGVycyBydWxlIQ==")
+	buf := bytes.NewBufferString("R29waGVycyBydWxlIQ==")
 	dec := base64.NewDecoder(base64.StdEncoding, buf)
 	io.Copy(os.Stdout, dec)
 	// Output: Gophers rule!