If curses, termcap or ncurses was not found, configure currently does not error out. This fixes that.
I'm only unsure about the wording here.
Instead of raising, we should just enable rb-readline instead of c-readline.
raise an error, when curses was not found
use rb-readline when curses was not found
raise rb-readline version to 0.4.2
This updates readline to 0.4.2 too, which was released one year ago. Since then, no new release came out, so I would say, that this is a good start.