(struct input_event): Add member `arg'.

(MENU_BAR_EVENT): Renamed from menu_bar_event.
(USER_SIGNAL_EVENT): Renamed from user_signal.

src/termhooks.h

@@ -283,7 +283,7 @@ enum event_kind
   selection_clear_event,	/* Another X client cleared our selection.  */
   buffer_switch_event,		/* A process filter has switched buffers.  */
   delete_window_event,		/* An X client said "delete this window".  */
-  menu_bar_event,		/* An event generated by the menu bar.
+  MENU_BAR_EVENT,		/* An event generated by the menu bar.
 				   The frame_or_window field's cdr holds the
 				   Lisp-level event value.
 				   (Only the toolkit version uses these.)  */
@@ -304,16 +304,18 @@ 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,
+  USER_SIGNAL_EVENT,		/* A user signal.
+                                   code is a number identifying it,
                                    index into lispy_user_signals.  */
 
-  /* Currently only returned when the mouse enters a tool-bar item that
-     has a help string.  Member frame_or_window of the input_event is
-     a cons cell whose car is the tool-bar's frame and whose cdr is the
-     help string.  */
+  /* Help events.  Member `frame_or_window' of the input_event is the
+     frame on which the event occurred, and member `arg' contains
+     the help to show.  */
   HELP_EVENT,
 
+  /* An event from a tool-bar.  Member `arg' of the input event
+     contains the tool-bar item selected.  If `frame_or_window'
+     and `arg' are equal, this is a prefix event.  */
   TOOL_BAR_EVENT,
 
   /* Queued from XTread_socket on FocusIn events.  Translated into
@@ -332,7 +334,6 @@ enum event_kind
 
 struct input_event
 {
-
   /* What kind of event was this?  */
   int kind;
   
@@ -359,6 +360,10 @@ struct input_event
   /* This field is last so that struct selection_input_event
      does not overlap with it.  */
   Lisp_Object frame_or_window;
+
+  /* Additional event argument.  This is used for TOOL_BAR_EVENTs and
+     HELP_EVENTs and avoids calling Fcons during signal handling.  */
+  Lisp_Object arg;
 };
 
 /* Called to read input events.  */