[v7 5/6] user32: Send WM_NCPAINT and WM_ERASEBKGND when window is shown and add tests

[Fabian Maurer]

> msg.c:5233: Test failed: RedrawWindow:show_popup_extreme_location:
> 12: the msg 0x001c was expected, but got msg 0x0085 instead

Can't reproduce the error.