(event_kind) [WINDOWSNT]: New event type: mouse_wheel.

src/termhooks.h

@@ -234,6 +234,23 @@ enum event_kind
 				   the mouse click occurred in.
 				   .timestamp gives a timestamp (in
 				   milliseconds) for the click.  */
+#ifdef WINDOWSNT
+  mouse_wheel,			/* A mouse-wheel event is generated by a 
+				   wheel on a mouse (e.g., MS Intellimouse).
+				   The event contains a delta that corresponds
+				   to the amount and direction that the wheel
+				   is rotated.  This delta is typically
+				   used to implement a scroll or zoom.
+				   .code gives the delta.
+				   .modifiers holds the state of the
+				   modifier keys.
+				   .x and .y give the mouse position,
+				   in characters, within the window.
+				   .frame_or_window gives the frame
+				   the wheel event occurred in.
+				   .timestamp gives a timestamp (in
+				   milliseconds) for the wheel event.  */
+#endif
   scroll_bar_click,		/* .code gives the number of the mouse button
 				   that was clicked.
 				   .modifiers holds the state of the modifier
@@ -284,6 +301,7 @@ struct input_event
   /* For an ascii_keystroke, this is the character.
      For a non_ascii_keystroke, this is the keysym code.
      For a mouse event, this is the button number.  */
+  /* In WindowsNT, for a mouse wheel event, this is the delta.  */
   int code;
   enum scroll_bar_part part;