bug#71376: 14.0.5; find-file-at-point doesn't work in LaTeX-mode

[Stefan Monnier]

> | Major mode for editing files of input for TeX, LaTeX, or SliTeX.
> | This is the shared parent mode of several submodes.
> | Tries to determine (by looking at the beginning of the file) whether
> | this file is for plain TeX, LaTeX, or SliTeX and calls ‘plain-tex-mode’,
> | ‘latex-mode’, or ‘slitex-mode’, accordingly.  If it cannot be determined,
> | such as if there are no commands in the file, the value of 
> ‘tex-default-mode’
> | says which mode to use.
> `----
>
> `tex-mode' redirects to submodes via `tex--redirect-to-submode'.  I
> think we ask the tex-mode.el maintainer.
>
> @Stefan: Should the entries in ffap.el for `tex-mode' be replaced by
> `plain-tex-mode' as well?

No buffer should be in `tex-mode` (it's an "abstract" parent mode), so
AFAICT the current entry

    (tex-mode . ffap-tex-mode)          ; search ffap-tex-path

in `ffap-alist` is not very useful.
So unless/until `ffap.el` is changed to pay attention to the modes'
hierarchy rather than just the value of `major-mode`, we should use
things like `plain-tex-mode`.


        Stefan