Not through interactive console, because it was printing prompts, while
`python <prog.py` does not emit anything:

    $ cat prog.py
    print 'Hello World'

    $ python <prog.py
    Hello World

    $ gpython <prog.py
    Python 2.7.18 (default, Apr 20 2020, 20:30:41)
    [GCC 9.3.0] [GPython 0.0.8] [gevent 20.9.0] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    (InteractiveConsole)
    Hello World

After the patch gpython output is the same as of python:

    $ gpython <prog.py
    Hello World

Test coverage for interactive mode is pending.
We'll add them soon in a follow-up patch after implementing -i.

For _interact - by this patch logic - we should be dropping custom
raw_input, since now _interact is called only when sys.stdin is tty.
But we'll soon be invoking _interact when stdin is not a tty (for
`gpython -i <prog.py`), so leave that logic in place as is.

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!15