encoding/gob: fix "// +build" comment for debug.go

R=golang-dev, rsc, adg, r, r
CC=golang-dev
https://golang.org/cl/5693060

src/pkg/encoding/gob/Makefile

-# Copyright 2009 The Go Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style
-# license that can be found in the LICENSE file.
-
-# Help for debugging.
-dump:	dump.go
-	go clean -i  # remove installed copy
-	go build -t gob-debug -o dump dump.go
-

src/pkg/encoding/gob/debug.go

@@ -3,14 +3,15 @@
 // license that can be found in the LICENSE file.
 
 // Delete the next line to include in the gob package.
-// +build gob-debug
+// +build ignore
 
 package gob
 
 // This file is not normally included in the gob package.  Used only for debugging the package itself.
-// Add debug.go to the files listed in the Makefile to add Debug to the gob package.
 // Except for reading uints, it is an implementation of a reader that is independent of
 // the one implemented by Decoder.
+// To enable the Debug function, delete the +build ignore line above and do
+//	go install
 
 import (
 	"bytes"

src/pkg/encoding/gob/dump.go

@@ -7,6 +7,7 @@
 package main
 
 // Need to compile package gob with debug.go to build this program.
+// See comments in debug.go for how to do this.
 
 import (
 	"encoding/gob"