bug#3580: 23.0.94; Info-documented variable dir-locals-class-alist does not exist

Info node "(elisp) Directory Local Variables" mentions this variable:

 -- Variable: dir-locals-directory-alist
     This alist holds directory names and their assigned class names.
     It is updated by `dir-locals-set-directory-class'.

As it says, function dir-locals-set-directory-class is supposed to
update that variable. To me it seems that the mentioned function updates
variable dir-locals-directory-cache instead of
dir-locals-directory-alist.

I "M-x rgrep'ed" the whole Emacs source repository and the only
occurences of dir-locals-directory-alist were these:

./info/elisp-2:4441: -- Variable: dir-locals-directory-alist
./lisp/ChangeLog:4997:	(dir-locals-directory-alist): Rename from
    `project-directory-alist'.
./doc/lispref/variables.texi:1764:@defvar dir-locals-directory-alist