Input: Add postdown to ButtonClassRec

This mirrors that in KeyClassRec: the state of the buttons as posted to
GetPointerEvents, rather than the state of the buttons as processed by
ProcessOtherEvent and friends.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

include/inputstr.h

@@ -181,6 +181,7 @@ typedef struct _ButtonClassRec {
     unsigned short	state;
     Mask		motionMask;
     CARD8		down[DOWN_LENGTH];
+    CARD8		postdown[DOWN_LENGTH];
     CARD8		map[MAP_LENGTH];
     union _XkbAction    *xkb_acts;
 } ButtonClassRec, *ButtonClassPtr;