bug#27999: 26.0.50; delete-other-windows deletes side windows

[martin rudalics]

> I believe this is due to commit b8fd71d57 (C-x 1 works fine when
> checking out its parent commit).

Right.

> I tested using the following:
>
> (display-buffer-in-side-window (get-buffer "*Messages*") '((side .
> left)))
>
> Executing "C-x 1" in Emacs 25.2 doesn't delete the *Messages* buffer,
> but in master it does.

Please read Eli's complaints in the discussion of bug#24368

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=24368

to understand why I made the change.  You now have to explicitly set the
'no-delete-other-window' parameter of a side window in order to preserve
it from being deleted.  This parameter works for any window, BTW.

I forgot to fix the doc-string of ‘delete-other-windows’ accordingly and
hopefully did that now.  Please have a look.

Thanks, martin