bug#27108: 26.0.50; tramp and recentf again

[Stephen Berman]

Starting with this change:

   commit dca22e86e02d16a31128c163925b13404f777c0f
   Author: Michael Albinus <michael.albinus@gmx.de>
   Date:   Wed May 24 16:16:53 2017 +0200
   
     Introduce a defstruct `tramp-file-name' as central data structure.

when I start emacs with recentf-mode enabled and the ~/.emacs.d/recentf
contains a tramp-sensitive entry, e.g. this:

--8<---------------cut here---------------start------------->8---
;;; Automatically generated by ‘recentf’ on Sat May 27 11:51:22 2017.

(setq recentf-list
      '(
        "/su:root@rosalinde:/etc/"
        ))

(setq recentf-filter-changer-current 'nil)


;; Local Variables:
;; coding: utf-8-emacs
;; End:
--8<---------------cut here---------------end--------------->8---

Emacs then prompts for the password for the file
"/su:root@rosalinde:/etc/".  Likewise for e.g. a remote file accessed
via sftp.

The problem also happens when I have the above recentf file and start
emacs like this: 

emacs -Q --eval "(custom-set-variables '(recentf-mode t))"

This recalls bug#26258 but now there is no error, just the login prompt.


In GNU Emacs 26.0.50 (build 28, x86_64-pc-linux-gnu, GTK+ Version 3.22.8)
 of 2017-05-27 built on rosalinde
Repository revision: 527a7cc9425370f7217a4d2b6914b96dff6f5ec1
Windowing system distributor 'The X.Org Foundation', version 11.0.11901000

Configured using:
 'configure 'CFLAGS=-Og -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix