Redirection of stdin results in panic on unrwrap()

Created by: OdysseusGE

For example echo ls | ./target/debug/ion results in:

thread 'main' panicked at 'called Result::unwrap() on an Err value: Os { code: 25, kind: Other, message: "Inappropriate ioctl for device" }', libcore/result.rs:916:5

The problematic unwrap is at src/lib/shell/binary/readln.rs:30. The ultimate problem is that liner tries to use a raw input mode, but this will fail for a redirected stdin.

Since I'm not sure where this problem should be fixed, I opened a similar issue at https://github.com/MovingtoMars/liner/issues/77 See also: https://github.com/ticki/termion/issues/39