bug#55329: [PATCH] Choose latex environment for table.el export

[Eli Zaretskii]

> From: Vladimir Nikishkin  <lockywolf@gmail.com>
> Date: Mon, 09 May 2022 10:30:57 +0800
> 
> The patch creates 1 new customize variable:
> 1. table-latex-environment
> 
> And changes the following 2 functions:
> 1. table--generate-source-epilogue
> 2. table--generate-source-prologue

Thanks.  A couple of minor nits:

> +(defcustom table-latex-environment "tabular"
> +  "Which tabular-compatible environment to use when generating latex.
> +tabular and longtable are known to work."

I'm not sure I understand the purpose of the last sentence, nor what
it adds to the doc string.

Also, perhaps we should prefer symbol values, not string values here?
Symbols are easier to compare and harder to make mistakes.