(BWDIC!) Drop readline(3) support..
I just stumbled over a, well, bug in the MLE (you can add history
entries even if *line-editor-disable*, tty_init() doesn't take
care for that, too; and more), and the readline(3) code also has
the same problems.
In my opinion there are just two things which makes readline(3)
preferable compared to MLE: the global resource file, and more
editor functions. We can't do anything about the first, but
i rather add more editor functions than stumbling over such bugs
and have to deal with multiple implementations, henceforth.