Added definition of SS_USERITEM.

diff --git a/include/winuser.h b/include/winuser.h
index 6c07a42..0fdab4e 100644
--- a/include/winuser.h
+++ b/include/winuser.h
@@ -2069,7 +2069,7 @@
 #define SS_BLACKFRAME       0x00000007L
 #define SS_GRAYFRAME        0x00000008L
 #define SS_WHITEFRAME       0x00000009L
-
+#define SS_USERITEM         0x0000000AL
 #define SS_SIMPLE           0x0000000BL
 #define SS_LEFTNOWORDWRAP   0x0000000CL