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.

include/wincurs.h

@@ -89,7 +89,6 @@ extern void curses_add_menu(winid wid, const glyph_info *,
                             const char *str, unsigned int itemflags);
 extern void curses_end_menu(winid wid, const char *prompt);
 extern int curses_select_menu(winid wid, int how, MENU_ITEM_P **selected);
-extern void curses_update_inventory(int);
 extern void curses_mark_synch(void);
 extern void curses_wait_synch(void);
 extern void curses_cliparound(int x, int y);
@@ -113,6 +112,8 @@ extern void curses_outrip(winid wid, int how, time_t when);
 extern void genl_outrip(winid tmpwin, int how, time_t when);
 extern void curses_preference_update(const char *pref);
 extern void curs_reset_windows(boolean, boolean);
+extern void curses_update_inventory(int);
+extern perminvent_info *curses_update_invent_slot(winid, int, perminvent_info *);
 
 /* curswins.c */