windows/registry: copy latest changes from internal/syscall/registry

This CL includes changes from:

http://golang.org/cl/9805
http://golang.org/cl/9806
http://golang.org/cl/9901

Change-Id: I1f41a8215f9f760c0d3b84596e37bf48bf4c9bc2
Reviewed-on: https://go-review.googlesource.com/10132
Reviewed-by: Rob Pike <r@golang.org>

windows/registry/export_test.go

@@ -0,0 +1,11 @@
+// Copyright 2015 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.
+
+// +build windows
+
+package registry
+
+func (k Key) SetValue(name string, valtype uint32, data []byte) error {
+	return k.setValue(name, valtype, data)
+}