[1/2] comctl32: add WM_PAINT message sequence tests

[Felix Nawothnig]

James Hawkins wrote:
> If you're subclassing the header control and checking messages from
> the header control, then you need to add another message sequence,
> HEADER_SEQ_INDEX.

Problem is I need to test whether the header msgs are sent between the 
WM_PAINT and WM_NOTIFY of the listview - right now the 
WM_PAINT/WM_NCPAINT/WM_ERASEBKGND _are_ sent - just not in between but 
after WM_PAINT processing (which causes the flickering).

I agree that the "hdr" flag is kinda hackish, any idea how to properly 
abstract away what I'm trying to do?

Felix