bug#22941: 25.1.50; epa-list-secret-keys does not find gpg private keys

[Iñigo Serna]

Since a couple of months ago emacs 25.0.x (last tested as 2016/03/08
from git master) can't open encrypted files (using symmetric keys), as
epa can't find secret keys from gpg.

This is the error message I get:
"""
Error while decrypting with "gpg":

gpg: encrypted with 2048-bit RSA key, ID C0ED9C8489B28C43, created 2016-01-12
      "Iñigo Serna (XXX.YY) <inigo@XXX.YY>"
gpg: decryption failed: No secret key
"""

I use gpg (not gpg2) so I added '(setq epg-gpg-program "gpg")' to my
configuration as new epa defaults to gpg2 when I've run "emacs -Q -nw".

`epa-list-secret-keys` does not find any keys.

This same configuration works ok with 24.5.1 (from Fedora 23 x86_64), and
even `epa-list-secret-keys` shows the private keys correctly.

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For information about debugging Emacs, please read the file
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In GNU Emacs 25.1.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.7)
 of 2016-03-08 built on inigo.katxi.org
Repository revision: 80864c2a04597d31ba453c9af69d35b15c4e1e24
System Description:     Fedora release 23 (Twenty Three)

Configured using:
 'configure --prefix=/usr/ --libdir=/usr/lib64 --sysconfdir=/etc
 --disable-static --prefix=/opt/emacs --with-xwidgets
 --with-x-toolkit=gtk3 CFLAGS=-Os'

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

Important settings:
  value of $LANG: en_GB.utf8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
"gpg"
Decrypting /home/inigo/personal/agenda/other.org.gpg...done
epa-file--find-file-not-found-function: Opening input file: Decryption failed, 
No secret key: C0ED9C8489B28C43
"gpg"

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired dired-loaddefs format-spec
rfc822 mml easymenu mml-sec password-cache gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils epa-file epa derived epg epg-config
term/xterm xterm time-date mule-util 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 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 term/tty-colors 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 obarray 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 91217 6511)
 (symbols 48 19819 0)
 (miscs 40 52 107)
 (strings 32 14550 4887)
 (string-bytes 1 415390)
 (vectors 16 9702)
 (vector-slots 8 371442 10588)
 (floats 8 171 795)
 (intervals 56 222 14)
 (buffers 976 13)
 (heap 1024 34449 1624))