go.tools: add copyright messages to source files.

R=r
CC=golang-dev
https://golang.org/cl/13305043
diff --git a/pointer/gen.go b/pointer/gen.go
index b13d47a..0d2e1bd 100644
--- a/pointer/gen.go
+++ b/pointer/gen.go
@@ -1,3 +1,7 @@
+// Copyright 2013 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.
+
 package pointer
 
 // This file defines the constraint generation phase.