kconfig/lxdialog: more portable and use ncurses from macports on MacOS

check-lxdialog.sh now correctly tests for ncurses and is a bit more portable.
On Darwin it uses the ncurses from macports.

 reporter_name="Harold Grovesteen"

 reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00052.html"

 reporter_comment=""