screen sequence doesn't work (like bios_console.c on some platforms).

the option config UI.

Introduce new {show,set,clear}_setting() that take a struct setting *
rather than a const char *.

set_setting() handles calling clear_setting() when appropriate, so that
individual setting types don't have to check for empty strings.

memory" and "no space left for DHCP options"

thinking that a command executed successfully.

call doesn't do it.

command is linked in.

printing in the bottom-right position.

calls.  This does make a visible difference when clearing the screen with
werase() inside bochs or qemu.

the (slow) werase().

stdscr directly.