There's not much point in running the entire terminal mode session
on top of libreadline or libedit, unless it is clear the session
is really running interactively on a terminal.

Thus, only use the libreadline/libedit version if stdin points to
a terminal. Otherwise, resort to the simple version without readline
support. That ensures everything works well when running it within
a pipeline.

GNU libreadline does not seem to have any issues when running on a
pipe as input, thus use it all the time.

EditLine (NetBSD, MacOS) has issues with that, so only use it when
running interactively on a terminal.

Besides of fixing a logico, this allows for a really straightforward
decision. All EditLine versions so far use 0x0402 as their version
number.