Avoid alignment problems with NMPGSCROLL struct.

include/commctrl.h

@@ -1808,6 +1808,8 @@ static const WCHAR WC_PAGESCROLLERW[] = { 'S','y','s','P','a','g','e','r',0 };
 #define PGN_SCROLL              (PGN_FIRST-1)
 #define PGN_CALCSIZE            (PGN_FIRST-2)
 
+#include "pshpack1.h"
+
 typedef struct
 {
     NMHDR hdr;
@@ -1819,6 +1821,8 @@ typedef struct
     INT  iScroll;
 } NMPGSCROLL, *LPNMPGSCROLL;
 
+#include "poppack.h"
+
 typedef struct
 {
     NMHDR hdr;