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

["積丹尼 Dan Jacobson" <jidanni@jidanni.org>]

Regarding

     ispell-help is an autoloaded compiled Lisp function in ‘ispell.el’.

     (ispell-help)

     Display a list of the options available when a misspelling is encountered.

     Selections are:

     DIGIT: Replace the word with a digit offered in the *Choices* buffer.
     SPC:   Accept word this time.
     ‘i’:   Accept word and insert into private dictionary.
     ‘a’:   Accept word for this session.
     ‘A’:   Accept word and place in ‘buffer-local dictionary’.
     ‘r’:   Replace word with typed-in value.  Rechecked.
     ‘R’:   Replace word with typed-in value.  Query-replaced in buffer.  Rechecked.
     ‘?’:   Show these commands.
     ‘x’:   Exit spelling buffer.  Move cursor to original point.
     ‘X’:   Exit spelling buffer.  Leaves cursor at the current point, and permits
             the aborted check to be completed later.
     ‘q’:   Quit spelling session (Kills ispell process).
     ‘l’:   Look up typed-in replacement in alternate dictionary.  Wildcards okay.
     ‘u’:   Like ‘i’, but the word is lower-cased first.
     ‘m’:   Place typed-in value in personal dictionary, then recheck current word.
     ‘C-l’:  Redraw screen.
     ‘C-r’:  Recursive edit.
     ‘C-z’:  Suspend Emacs or iconify frame.

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.