VC mode doesn't handle 'su' user changes correctly

[Alan Morgan <arm@camcon.co.uk>]

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In GNU Emacs 21.2.2 (sparc-sun-solaris2.6, OSF/Motif Version 1.2.6)
 of 2002-08-08 on athene
configured using `configure  --with-x-toolkit=motif --prefix=/usr/local/src/edcad/gnu'
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: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

This bug occurs when one changes user using the su commmand, then starts an
emacs and edits a file which is under version control. The same behaviour is
seen for both CVS and SCCS, but I haven't tried under RCS. These observations
were made using emacs 21.2 running on a Solaris 2.8 machine. This problem does
not occur in emacs version 20.2.1.

As an example to show the bug, I do the following:

1. log in as user arm
2. 'su c5827' - c5827 is a 'project' userid
3. start emacs as user c5827, using emacs -q to ensure this isn't problem with
   something in my .emacs file.
4. In emacs, find the file
   /home/c5827/emacs/vc_bug.txt
  - this file is owned by user c5827, in a directory owned by c5827 and under
  SCCS source control.
5. check out the file with C-x C-q - the buffer becomes writeable
6. Make some change to the file
7. Save it C-x C-s
8. Attempt to check it back in with C-x C-q

At this point, VC mode seems to get confused about userids. It responds with
 
Steal the lock on /home/c5827/emacs/vc_bug.txt:1.2 from c5827? (yes or no)

Even if I say yes to this, and send the required email to c5827, VC mode still
fails to check the file back in, with error:

ERROR [../c5827/emacs/SCCS/s.vc_bug.txt]: specified SID not in p-file (un3)

Performing the exact same series of actions under emacs 20.2.1 checks the file
back into SCCS (as user c5827) without any problems, so it appears something
has changed recently to cause this bug.

Best Regards,

Alan

-- 
Dr Alan Morgan             |                                 
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