bug#3789: 23.0.95; confusion with EasyPG/vc interaction

If you have a .gpg file that is encrypted using a key that you don't
have in your keyring, EasyPG reports

File exists, but cannot be read

and gives you an empty buffer.  This is probably reasonable behavior,
though I would be happier if it handled it in the same way as a file
that you really don't have read permission on, since this reduces the
likelihood of clobbering it making the buffer writable and saving.  Not
a big deal.

If, however, that file is checked into RCS, EasyPG asks

File whatever.gpg was lost; check out from version control? (yes or no)

and then falls back to

File exists, but cannot be read.

This is pretty easy to reproduce.  Create a file and encrypt it using a
public key for which you don't have a private key.  Now kill the buffer
and, outside of emacs, do

mkdir RCS
ci -u file.gpg

Now, back in emacs, do C-x C-f on the file, and observe the behavior I
have described.

All this can be reproduced with emacs 23.0.95 run as emacs -q.



In GNU Emacs 23.0.95.1 (i686-pc-linux-gnu, GTK+ Version 2.10.4)
 of 2009-06-23 on motoko.argon.local
Windowing system distributor `The X.Org Foundation', version 11.0.70101000
configured using `configure  '--prefix=/opt/tps/packages/linux.ix86.rhel5/emacs-23.0.95-1''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Text

Minor modes in effect:
  diff-auto-refine-mode: t
  which-function-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t

Recent input:
<return> M-x r e p o r t SPC e m SPC b SPC <return
>

Recent messages:
Mark set [2 times]
Mark saved where search started
Mark set [3 times]
Saving file /home/jberkenb/argon/information/general/.upass.gpg...
stdin: 0% (0/0)
stdin: 0% (2044/0)
Wrote /home/jberkenb/argon/information/general/.upass.gpg [2 times]
Mark set [2 times]
/home/jberkenb/argon: 0% (0/1374)
/home/jberkenb/argon: 100% (1374/1374)