icmd is not usable when the tested binary expects a console

[apostasie]

Assume you want to pass along a pty, because the binary you are testing expects a console.

Since icmd does replace stdout with an io.Multiwriter, this won't work.
icmd should not do that, or at least expose a way for the user to prevent icmd from doing it (eg: io.Copy would be a better approach)

I appreciate this might be a minority case that icmd does not want to cover, but then, current implementation feels wrong.

[apostasie]

@dnephin let me take another look at that and confirm.