Major tidy up of Scroll.c to add foundations for flatscroll bars

[Alexandre Julliard]

"Andrew M. Johnston" <johnstonam at logica.com> writes:

> With these observations in mind,  I think the suggested approach becomes
> 
> 1. Remove the non api entry points into scrollbar,  the first patch I sent does this for mdi
>     But another is needed for nonclient.c
> 2. Make all the drawing paths use paint messages internally so they can be picked up by the
>    subclassed window when it is a flatSB.
> 3. Implement flatSB by subclassing the window and process the WM_PAINT messages differently

The thing is we cannot pick any implementation we like, we have to do
it the Windows way. So using messages internally is only acceptable in
cases where Windows does it that way. The native flatsb code has to
work on top of our scrollbars, and our flatsb implementation should
work on Windows too.

-- 
Alexandre Julliard
julliard at winehq.com