comctl32: Update header window in listview WM_PAINT handler.

[Aric Stewart]

The commit 9badfb50cf38e930372d721450581f4597af86c2 is causing
  an application I am working on (ichitaro) to behave very poorly. It 
cause the file->open dialog to repaint incorrectly (screen shots attached)

I downloaded utorrent to see the original bug and I do not see the 
flickering that you where trying to fix. Since you fixed this recently 
do you have some insight on why the UpdateWindow is causing this issue?

-aric