bug#50776: add "ispell show where we looked" command

[Eli Zaretskii]

> From: 積丹尼 Dan Jacobson
>  <jidanni@jidanni.org>
> Date: Fri, 24 Sep 2021 21:20:39 +0800
> 
> Please add one more:
> Show all the dictionaries that were checked when looking for (and not
> finding) the word.
> 
> That way one could figure out why e.g., "jitter" is misspelled in emacs,
> but not in the shell's ispell.
> 
> Sure, there are various alists, but we want to see where it really looked.

I don't understand: there's only one dictionary, the current one.