groundwork for an interface change

Add a new window-port interface function
     perminvent_info *
     update_invent_slot(winid window, int slot, perminvent_info *);

That should be nice and flexible and allow exchanges of useful
information between the core and the window port. Information
to be exchange can be easily modified in include/wintype.h as
things evolve.

Information useful to the core can be exchanged from the
window-port in struct to_core.

Information useful from the core to the window-port can be
passed in struct from_core.

I'm not going to update any docs until much later after things
are fully working and settled.

This also doesn't fix or have anything to do with existing
TTY_PERM_INVENT issues.

win/curses/cursmain.c

@@ -77,7 +77,6 @@ struct window_procs curses_procs = {
     curses_end_menu,
     curses_select_menu,
     genl_message_menu,
-    curses_update_inventory,
     curses_mark_synch,
     curses_wait_synch,
 #ifdef CLIPPING
@@ -117,6 +116,8 @@ struct window_procs curses_procs = {
     genl_status_enablefield,
     curses_status_update,
     genl_can_suspend_yes,
+    curses_update_inventory,
+    curses_update_invent_slot,
 };
 
 /*
@@ -693,6 +694,17 @@ curses_update_inventory(int arg)
     }
 }
 
+perminvent_info *
+curses_update_invent_slot(
+    winid window UNUSED,  /* window to use, must be of type NHW_MENU */
+    int inventory_slot UNUSED,          /* slot id: 0 - info return to core */
+                                        /*          1 - gold slot */
+                                        /*          2 - 29 obj slots */
+    perminvent_info *pi UNUSED)
+{
+    return (perminvent_info *) 0;
+}
+
 /*
 mark_synch()    -- Don't go beyond this point in I/O on any channel until
                    all channels are caught up to here.  Can be an empty call