Doesn't build without modification on systems with ncursesw as default ncurses

[qguv]

82f3638 breaks the build on modern systems that use ncursesw as the default ncurses. Rather than force a definition of CREDDIT_USE_NCURSESW on non-mac systems, it would be nice it were left for the user to define (or not) when running make. Alternatively, creddit.mk could detect whether an ncursesw/ directory exists in any includes dir. Unfortunately I don't know enough mk to make this change myself.