[PATCH resend 1/2] user32: Fix WM_NCPAINT for windows crossing screen boarders and add tests

[Fabian Maurer]

> This won't be correct for multi-monitor setups. That sort of thing
> should probably be handled on the server side.

You're right, we should take care of that, too.
Sadly, I don't have a multi monitor setup to run tests with.
An idea how to still work on this?

Regards,
Fabian Maurer