Usernames with @ signs break "file being modified by another user" lock symlinks

[Owen Jacobson]

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In GNU Emacs 21.2.1 (powerpc-apple-darwin8.0)
 of 2007-05-08 on s11-cp04-07.corp.kazootek.com
configured using `configure  --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --disable-dependency-tracking --without-x'
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: nil
  locale-coding-system: nil
  default-enable-multibyte-characters: t

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

1.  Create a username* with an @ symbol in it (eg "test@localhost") and su
to it.
2.  emacs test.txt
3.  Enter some text and attempt to save it.

Emacs will warn that the file is in use by another process and report
its own PID, despite being the only editor accessing the file.  Examining
the output of ls -l while this prompt is displayed shows a symlink named
.#filename, linked to test@localhost@MACHINENAME.PID

I've verified this on a linux system with a normal local user named
"test@localhost" as well; this is not dependant on directory-based
usernames.

* This came up because the machine I normally use, a Mac, has been
  bound into an OpenDirectory domain and my username (as seen in $USER
  and friends) is ojacobson@DOMAIN.COM.