test: add rotate.go and fixedbugs/bug313

Update #4139.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7094047

test/rotate2.go

@@ -0,0 +1,12 @@
+// runoutput ./rotate.go
+
+// 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.
+
+// Generate test of bit rotations.
+// The output is compiled and run.
+
+package main
+
+const mode = 2