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>
3 files changed