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

[martin rudalics]

> The regression appears to be that the synchronisation of buffer local
> and global values doesn't work.  When I type M-x, then C-h v
> print-escape-newlines, I get this:
>
> print-escape-newlines is a variable defined in ‘C source code’.
> Its value is nil
> Local in buffer  *Minibuf-1*; global value is t
>
> Which doesn't make sense (the values are swapped).

The problem is with

2018-06-03  Stefan Monnier  <monnier@iro.umontreal.ca>

        Fix bug#30846, along with misc cleanups found along the way

and in particular

        Don't call swap_in_symval_forwarding since the currently swapped
        binding is never one we've modified.

I don't care how it gets fixed but it should get fixed, for example,
as in the attached patch.  Bugs like this can make people spend hours
of debugging all sorts of completely unrelated areas which is no fun.

So please, pretty please review that entire patch again - maybe it
contains additional sorts of problems.

Thank you in advance, martin

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