curses: save/restore message history

Have the curses interface save and restore message history for use
by ^P.  It doesn't spit the saved messages out into the visible
message window after restore; that's too distracting.

include/wincurs.h

@@ -222,6 +222,8 @@ extern void curses_init_mesg_history(void);
 extern void curses_teardown_messages(void);
 extern void curses_prev_mesg(void);
 extern void curses_count_window(const char *count_text);
+char *curses_getmsghistory(BOOLEAN_P);
+void curses_putmsghistory(const char *, BOOLEAN_P);
 
 #endif  /* WINCURS_H */