Added proper support for storing window parents in the server.
Added a few requests to query the window hierarchy.

diff --git a/server/user.h b/server/user.h
index 1e33168..d53cc53 100644
--- a/server/user.h
+++ b/server/user.h
@@ -33,5 +33,6 @@
 /* window functions */
 
 extern void destroy_thread_windows( struct thread *thread );
+extern int is_child_window( user_handle_t parent, user_handle_t child );
 
 #endif  /* __WINE_SERVER_USER_H */