bug#22747: 25.0.91; Customizing epg-gpg-program makes Gnus nnimap fail

[Teemu Likonen]

When variable epg-gpg-program is customized to "gpg2" and saved through
Emacs customize interface (M-x customize-option RET epg-gpg-program RET)
Gnus nnimap method no longer works.

Example: When Gnus is started (M-x gnus) all my nnimap settings fail
with this message in *messages* buffer:

    Warning: Opening nnimap server on opettaja...failed: ; Unable to open
    server nnimap+opettaja due to: GPG error: "no usable configuration",
    OpenPGP; [...]

It started happening after this commit:

    commit e80c2a7b47d161f00aac096b9d58a18879a122e8
    Author: Daiki Ueno <ueno@gnu.org>
    Date:   2016-02-17 16:32:25 +0900

        Make GnuPG version check robuster

        We changed the default gpg program to "gpg2" from "gpg" in the commit
        f93d669a16bd3cb3f43f0c8cfd22fe18b627a6a1.  However, there are two
        maintained branches (2.0 and 2.1) and Emacs doesn't work well with 2.0
        series.  Check the actual version of "gpg2" at run time, and properly
        divert to "gpg" if necessary.
        * lisp/epg-config.el: Require 'cl-lib for `cl-destructuring-bind'.
        (epg-config--program-alist): New variable.
        (epg--configurations): New variable.
        (epg-configuration-find): New function.
        (epg-config--make-gpg-configuration): New function.
        (epg-config--make-gpgsm-configuration): New function.
        (epg-configuration): Mark as obsolete.
        * lisp/epg.el (epg-context): Use `epg-configuration-find'.

In GNU Emacs 25.0.91.6 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
 of 2016-02-20 built on mithlond
Repository revision: d675db943e8e55321a58353600d3574a8433c52d
Windowing system distributor 'The X.Org Foundation', version 11.0.11604000
System Description:     Debian GNU/Linux 8.3 (jessie)

Configured using:
 'configure --prefix=/home/dtw/local --with-x-toolkit=gtk3
 --with-xwidgets --with-wide-int'

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

Important settings:
  value of $LC_MESSAGES: C
  value of $LANG: fi_FI.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: Group

Minor modes in effect:
  diff-auto-refine-mode: t
  gnus-topic-mode: t
  gnus-undo-mode: t
  ido-everywhere: t
  global-undo-tree-mode: t
  show-paren-mode: t
  winner-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
imap: Authenticating to ‘mail.kapsi.fi’ using ‘login’...done
Fetching from INBOX...
Reading incoming mail from file...
nnml: Reading incoming mail (no new mail)...done
Reading active file via nnml...done
Reading active file from arkisto via nnml...
Opening nnml server on arkisto...done
Reading active file from arkisto via nnml...done
Checking new news...done
No news is good news

Load-path shadows:
~/.emacs.d/omat/elisp/loaddefs hides 
/home/dtw/local/share/emacs/25.0.91/lisp/loaddefs

Features:
(shadow sort gnus-cite mail-extr nnir emacsbug sendmail imap utf-7 vc
vc-dispatcher paredit bs cus-edit cus-start cus-load vc-git diff-mode
gnus-topic nndraft nnmh nnagent epa-file epa network-stream nsm
auth-source starttls nnml nnmbox nnnil gnus-agent gnus-srvr gnus-score
score-mode nnvirtual gnus-msg gnus-art mm-uu mml2015 mm-view mml-smime
smime password-cache dig mailcap nntp gnus-cache gnus-bogofilter
gnus-sum gnus-group gnus-undo gnus-start gnus-cloud nnimap nnmail
mail-source tls gnutls utf7 netrc nnoo parse-time gnus-spec gnus-int
gnus-range message dired format-spec rfc822 mml mml-sec epg mm-decode
mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums
mailabbrev gmm-utils mailheader gnus-win gnus gnus-ems nnheader
gnus-util mail-utils mm-util help-fns mail-prsvr wid-edit ido seq
undo-tree diff paren winner rx slime-fancy slime-trace-dialog
slime-fontifying-fu slime-package-fu slime-references
slime-compiler-notes-tree slime-scratch slime-presentations advice
bridge slime-mdot-fu slime-enclosing-context slime-fuzzy
slime-fancy-trace slime-fancy-inspector slime-c-p-c
slime-editing-commands slime-autodoc slime-repl elp slime-parse slime
derived gud apropos compile etags xref cl-seq project eieio byte-opt
bytecomp byte-compile cl-extra help-mode cconv eieio-core arc-mode
archive-mode noutline outline easy-mmode pp comint ansi-color ring
hyperspec cl-macs thingatpt browse-url cl gv slime-autoloads edmacro
kmacro cl-loaddefs pcase cl-lib finder-inf tex-site info package
easymenu epg-config server time-date mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame 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 charscript case-table epa-hook jka-cmpr-hook help
simple abbrev minibuffer 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
dbusbind inotify dynamic-setting system-font-setting font-render-setting
xwidget-internal move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 357661 47827)
 (symbols 48 42292 0)
 (miscs 40 386 427)
 (strings 32 83688 10149)
 (string-bytes 1 2526766)
 (vectors 16 40829)
 (vector-slots 8 1477453 203150)
 (floats 8 520 407)
 (intervals 56 519 100)
 (buffers 976 43)
 (heap 1024 119244 7216))