bug#34318: 26.1.90; Strange behavior of two line message with running shell

[martin rudalics]

> For me, with no shell involved, in emacs-26 but not master:
>
> emacs -Q
>
> Type in scratch:
>
> (message "1\n2")
>
> Press C-x C-e
>
> -> two line message
>
> Now type:
>
> M-: (message "1\n2")
>
> -> one line message "1\n2".
>
> Now repeating C-x C-e on the original expression in scratch also
> produces a one line message, forever more.

Ahh...  This is a correct and considerably simpler scenario than the
one I provided.  Hence anyone investigating this issue, please stick
to Glenn's scenario.

Many thanks, martin