This causes the documented-slow cp2u() to be called in a loop, which
fortunately doesn't have very many iterations. If this is too slow,
then cp2u() can be rewritten, or the hotkeys can be cached in struct
widget or struct widget_data.
Note that check_kbd_label_key() does not yet allow non-ASCII
characters when CONFIG_UTF_8 is defined. Before they are allowed,
menu.c should also be updated.
Preparation for using struct terminal in formating functions.
By now distinguish between formating widgets and formating widgets with
displaying was done with term == NULL and term != NULL. I hope I'am
not wrong.
Introduce the macros before_widgets and foreach_widget_back. Use the
latter in update_all_widgets instead of foreach_widget so that the
widgets are printed in reverse order, which means that any listbox is
drawn last, which allows it to grab the cursor from the selected button
when the dialogue box is initialised or redrawn.
Requested by Kirk Reiser for great usability with screen readers.
