bug#42845: 27.1; Regression regarding supported gnupg versions

[APEL Martin]

If you run
    (epg-find-configuration 'OpenPGP t)
in emacs 27.1 on CentOS 7, it returns nil, whereas running the same
command in emacs 26.3 on the same machine returns a valid
configuration. This seems to be due to the management of supported GnuPG
versions. On CentOS 7, /usr/bin/gpg is a symlink to /usr/bin/gpg2 and
both report 2.0.22 as their version number. In 26.3 emacs used to
fallback to the gpg executable, as 2.0.22 was deemed good enough for
gpg, which
is not the case for 27.1 anymore. I didn't see any note regarding
changed requirements for GnuPG in the news file, so I don't think, that
this change is intentional.


In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30,
cairo version 1.15.12)
  of 2020-08-13 built on dell248cem
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: CentOS Linux 7 (Core)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
nil
Mark set [2 times]

Configured using:
  'configure --program-suffix=-27.1 --with-cairo'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS PDUMPER GMP

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

Major mode: Lisp Interaction

Minor modes in effect:
   tooltip-mode: t
   global-eldoc-mode: t
   eldoc-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
gnus-util rmail rmail-loaddefs text-property-search seq byte-opt gv
bytecomp byte-compile cconv mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils time-date subr-x cl-loaddefs
cl-lib epg-config tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type 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 elisp-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame minibuffer cl-generic
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 charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 44549 6978)
  (symbols 48 6088 1)
  (strings 32 15609 1844)
  (string-bytes 1 510452)
  (vectors 16 9334)
  (vector-slots 8 127780 9484)
  (floats 8 19 54)
  (intervals 56 184 0)
  (buffers 1000 11)
  (heap 1024 13064 1097))
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