bug#41423: 27.0.91; eshell file completion in tramp dir is slow (3 minutes) [regression on pretest]

[Gregory Heytings]

> > I just checked, and see no visible improvement.
>
> The first time you try completion, there's no difference. The cache must 
> be filled. But all next times you complete, it shall be faster for 
> remote directoriues.

Yes, this is what I did.  The first time there was no difference.  The 
second time I did not see any difference either, alas.  I just tried it 
again.

> I do not claim my patch is the solution. But it shall be useful, if 
> eshell-complete-commands-list is called somewhere.

A much better patch at this point is to just restore the previous default 
behavior (in Emacs 26 and earlier) by setting 
completion-at-point-functions to '(pcomplete t) instead of 
'(pcomplete-completions-at-point t), for example with:

(add-hook 'eshell-mode-hook (function (lambda () (setq 
completion-at-point-functions '(pcomplete t)))))

pcomplete is obsolete, but it is still there, and it works.