(event_kind): Add user_signal.

src/termhooks.h

@@ -284,7 +284,7 @@ enum event_kind
   deiconify_event,		/* An X client deiconified this window.  */
   menu_bar_activate_event,       /* A button press in the menu bar
 				   (toolkit version only).  */
-  drag_n_drop			/* A drag-n-drop event is generated when
+  drag_n_drop,			/* A drag-n-drop event is generated when
 				   files selected outside of Emacs are dropped
 				   onto an Emacs window.
 				   Currently used only on Windows NT.
@@ -297,6 +297,9 @@ enum event_kind
 				   the filenames of the dropped files.
 				   .timestamp gives a timestamp (in
 				   milliseconds) for the click.  */
+  user_signal			/* A user signal.
+				   .code is a number identifying it,
+				   index into lispy_user_signals.  */
 };
 
 /* If a struct input_event has a kind which is selection_request_event