Should include 'winspool.h'.

diff --git a/include/windows.h b/include/windows.h
index 79ff537..de9474a 100644
--- a/include/windows.h
+++ b/include/windows.h
@@ -19,6 +19,7 @@
 #include "winnls.h"
 #include "objbase.h"
 #include "mmsystem.h"
+#include "winspool.h"
 
 #if 0
   Where does this belong? Nobody uses this stuff anyway.