exp/norm: fix build by adding a test placeholder

R=golang-dev, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/4838050

src/pkg/exp/norm/norm_test.go

+// Copyright 2011 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 norm_test
+
+import (
+	"testing"
+)
+
+func TestPlaceHolder(t *testing.T) {
+	// Does nothing, just allows the Makefile to be canonical
+	// while waiting for the package itself to be written.
+}