curses menu: support backspace/delete for counts

Have curses call the core get_count() routine instead rolling its
own so that backspace and delete are supported.  That part was
trivial to accomplish.  Unfortunately it brought the disappearing
menu phenomenon back so it became more complicated overall.

win/curses/cursmesg.c

@@ -460,6 +460,10 @@ curses_count_window(const char *count_text)
 
     mvwprintw(countwin, 0, 0, "%s", count_text);
     wrefresh(countwin);
+    if (activemenu) {
+        touchwin(activemenu);
+        wrefresh(activemenu);
+    }
 }
 
 /* Gets a "line" (buffer) of input. */