Provide a way to communicate additional behaviors and/or appearances
desired from NetHack window port menus.
This is foundation work for changes to follow at a future date.
groundwork only - window port interface change
This changes the last parameter for add_menu() from a boolean
to an unsigned int, to allow additional itemflags in future
beyond just the "preselected" that the original boolean offered.
There shouldn't be any functionality changes with this groundwork-only
change, and if there are it is unintentional and should be reported.