Implemented GetAncestor and removed WIN_GetTopParent.
Removed a few more accesses to the WND structure.

diff --git a/windows/message.c b/windows/message.c
index 99a276c..2134854 100644
--- a/windows/message.c
+++ b/windows/message.c
@@ -433,7 +433,7 @@
         (raw_message == WM_RBUTTONDOWN) ||
         (raw_message == WM_MBUTTONDOWN))
     {
-        HWND hwndTop = WIN_GetTopParent( msg->hwnd );
+        HWND hwndTop = GetAncestor( msg->hwnd, GA_ROOT );
 
         /* Send the WM_PARENTNOTIFY,
          * note that even for double/nonclient clicks