anchor.diff:  *DEFAULT-FILE-PATH-DEFAULTS*.
   
   SETF CURRENT-DIRECTORY changes the operating system's current
  -directory to the PATHSPEC.  An error is signalled if the PATHSPEC
  -is wild or does not designate a directory."
  +directory to the PATHSPEC.  An error is signalled if PATHSPEC
  +is not a directory."
     (let ((cwd (%sys-getcwd)))
       (if cwd
           (parse-file-path cwd :expand-user nil)
  
positive.code: returned file-path is relative to the link, not
  *DEFAULT-FILE-PATH-DEFAULTS*.
  
  Signals an error if PATHSPEC is wild, or does not designate a
  symbolic link."
    ;; Note: the previous version tried much harder to provide a buffer
    ;; big enough to fit the link's name.  OTOH, NIX:READLINK stack
    ;; allocates on most lisps.
  
negative.code: Relative targets are resolved against the link.  Relative links
  are resolved against *DEFAULT-FILE-PATH-DEFAULTS*.
  
  Signals an error if target does not exist, or link exists already."
    (let ((link (file-path link))
          (target (file-path target)))
      (with-current-directory (absolute-file-path *default-file-path-defaults* nil)
  