Write registry values directly to avoid Path environment variable truncation.

[hamflx]

platform: Windows

the problem:

before setup	after setup

setx will truncate the path to 1024 characters. see https://superuser.com/a/387625

This PR directly uses writing registry values instead of spawning the setx command.

[hamflx]

@Classicrichblog Friendly ping on this, let me know if it needs a rebase