bug#60809: 29.0.60; eww-open-file ignores prefix argument

[Mike Kupfer <kupfer@rawbw.com>]

I can do C-u M-x eww RET to get a new eww buffer.  I would expect 
C-u M-x eww-open-file RET to also give me a new eww buffer.  Instead,
it reuses the existing eww buffer.

(The repo revision below includes a couple private changes to MH-E.
It's based on a14821d615.)

In GNU Emacs 29.0.60 (build 6, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw scroll bars) of 2023-01-10 built on alto
Repository revision: f26689637923ac9b834a209e1bab09c779be212f
Repository branch: emacs-29-mdk
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured using:
 'configure --prefix=/usr/new'

Configured features:
CAIRO FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG LIBSELINUX
LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM LUCID ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
  server-mode: t
  shell-dirtrack-mode: t
  delete-selection-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  column-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow mh-identity emacsbug display-line-numbers ediff ediff-merg
ediff-mult ediff-wind ediff-diff ediff-help ediff-init ediff-util info
shortdoc help-fns radix-tree sgml-mode facemenu wdired smerge-mode diff
diff-mode easy-mmode sort gnus-async gnus-bcklg gnus-kill gnus-ml
disp-table timezone url-http url-gw url-cache url-auth url-handlers
nnrss nndoc nndraft network-stream nsm gnus-agent gnus-srvr nnvirtual
nntp gnus-cache misearch multi-isearch flow-fill org-element org-persist
org-id org-refile avl-tree generator oc-basic cl-extra help-mode ol-eww
eww xdg url-queue mm-url ol-rmail ol-mhe ol-irc ol-info ol-gnus nnselect
ol-docview doc-view filenotify jka-compr image-mode exif ol-bibtex
bibtex ol-bbdb ol-w3m ol-doi org-link-doi org ob ob-tangle ob-ref ob-lob
ob-table ob-exp org-macro org-src ob-comint org-pcomplete org-list
org-footnote org-faces org-entities ob-emacs-lisp ob-core ob-eval
org-cycle org-table ol rx org-fold org-fold-core org-keys oc
org-loaddefs find-func cal-menu calendar cal-loaddefs org-version
org-compat org-macs format-spec view dired-aux dired-x pp mh-search
mh-letter textsec uni-scripts idna-mapping ucs-normalize uni-confusable
textsec-check shr-color color qp mm-archive mh-alias mail-extr mh-mime
mh-show goto-addr thingatpt gnus-cite mule-util mh-thread mh-inc hl-line
mh-tool-bar mh-acros mh-seq mh-xface mh-utils mh-folder which-func imenu
files-x mdk-mail gnus-mh gnus-msg mh-comp mh-scan mh-gnus gnus-dup nnmh
gnus-score score-mode gnus-art mm-uu mml2015 mm-view mml-smime smime
gnutls dig gnus-sum shr pixel-fill kinsoku url-file svg dom browse-url
url url-proxy url-privacy url-expand url-methods url-history url-cookie
generate-lisp-file url-domsuf url-util url-parse auth-source cl-seq
eieio eieio-core cl-macs json map gv url-vars gnus-group gnus-undo
gnus-start gnus-dbus dbus xml gnus-cloud nnimap nnmail mail-source utf7
nnoo parse-time iso8601 gnus-spec gnus-int gnus-range gnus-win gnus
nnheader range wid-edit mh-e mh-buffers mh-loaddefs message sendmail
mailcap yank-media puny dired dired-loaddefs rfc822 mml mml-sec
password-cache epa derived epg rfc6068 epg-config gnus-util
text-property-search time-date mm-decode mm-bodies mm-encode mail-parse
rfc2231 rfc2047 rfc2045 mm-util ietf-drums mail-prsvr mailabbrev
mail-utils gmm-utils mailheader server noutline outline icons cc-mode
cc-fonts cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars
cc-defs byte-opt bytecomp byte-compile shell subr-x pcomplete comint
ansi-osc ansi-color ring xcscope advice delsel vc vc-dispatcher
timeclock cl-loaddefs cl-lib mdk-hacks rmc iso-transl tooltip cconv
eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd
fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads inotify dynamic-setting
system-font-setting font-render-setting cairo x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 522609 92526)
 (symbols 48 31400 1)
 (strings 32 135287 10227)
 (string-bytes 1 4997054)
 (vectors 16 86279)
 (vector-slots 8 1888794 164946)
 (floats 8 549 679)
 (intervals 56 18934 107)
 (buffers 976 40))