user32: Notify explorer when the active window changes.

Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/user32/focus.c

@@ -154,6 +154,8 @@ static BOOL set_active_window( HWND hwnd, HWND *prev, BOOL mouse, BOOL focus )
         SendMessageW( hwnd, WM_ACTIVATE,
                       MAKEWPARAM( mouse ? WA_CLICKACTIVE : WA_ACTIVE, IsIconic(hwnd) ),
                       (LPARAM)previous );
+        if (GetAncestor( hwnd, GA_PARENT ) == GetDesktopWindow())
+            PostMessageW( GetDesktopWindow(), WM_PARENTNOTIFY, WM_NCACTIVATE, (LPARAM)hwnd );
     }
 
     /* now change focus if necessary */