For options ncurses and ncursesw, set USE_NCURSES=yes, on the assumption
that explicitly forcing ncurses does not mean "use builtin curses anyway"
unless the builtin curses is *really* ncurses.

(Yes, the ncursesw builtin.mk responds to USE_NCURSES and not USE_NCURSESW;
whether that's a bug is for someone else to decide.)

(dholland)