bug#46351: 28.0.50; Add convenient way to bypass Eshell's own pipelining

[Eli Zaretskii <eliz@gnu.org>]

> From: Sean Whitton <spwhitton@spwhitton.name>
> Cc: michael.albinus@gmx.de, 46351@debbugs.gnu.org
> Date: Thu, 20 Jan 2022 15:16:20 -0700
> 
> >> Okay, so I should add something to skip over my parsing code in the case
> >> that the first thing in the input is a redirection?
> >
> > I'm not sure I understand the intent: what do you want to accomplish
> > by this special handling?
> 
> Perhaps I misunderstood your earlier message.  I thought that you were
> saying that because Eshell does not support redirections at the very
> beginning of the line at present, my new syntax should not support that
> either, to prevent confusion.  Did you mean something else when you
> wrote "if it doesn't work now, then we cannot break it?"

I meant that if Eshell doesn't support that syntax, you can do
whatever you want in that case.  You don't need to make any effort to
support it, and you don't need to make any effort not to support it:
whatever your code does in that case will be OK.