bug#21595: 11.88.8; TeX help in Plain contaminated by LaTeX

[jfbu]

Remember to cover the basics, that is, what you expected to happen and
what in fact did happen.

The following TeX source file

    \def\foo{\begingroup\foo}\foo

    \bye

when run from a TeX-mode Emacs/AUCTeX buffer generates on C-c `,
after compilation has halted on a TeX capacity exceeded error,
a buffer displaying a long text of which I reproduce only the start
here:

ERROR: TeX capacity exceeded, sorry [grouping levels=255].

--- TeX said ---
\foo ->\begingroup
                   \foo
l.1 \def\foo{\begingroup\foo}\foo
                                 
--- HELP ---
TeX has just run out of space and aborted its execution. Before you
panic, remember that the least likely cause of this error is TeX not
having the capacity to process your document.  It was probably an
error in your input file that caused TeX to run out of room. The
following discussion explains how to decide whether you've really
exceeded TeX's capacity and, if so, what to do. If the problem is an
error in the input, you may have to use the divide and conquer method
described previously to locate it. LaTeX seldom runs out of space on a
short input file, so if running it on the last few pages before the
error indicator's position still produces the error, then there's
almost certainly something wrong in the input file.

The end of the error indicator tells what kind of space TeX ran out
of. The more common ones are listed below, with an explanation of
their probable causes.

buffer size
===========
Can be caused by too long a piece of text as the argument

[continued]

The rest of the text has many many references to LaTeX.

As the context here is Plain TeX this longish info is mostly
irrelevant (it provides useful information to average LaTeX
users, but nothing spicy to well trained macro programmers ;-) )

For some years I thought that the message originated in the
help system of the tex binary itself (my Emacs is configured
actually to run etex not tex if that matters), but it appears
that I could very well
have erred completely. I of course realized Knuth would not
have included such a message, but perhaps the binaries of
my TeXLive installation did provide an extended help system.

A guru from the LaTeX3 team tells me it can't be the case,
thus my question is

   Does the message somehow come from AUCTeX ?

Perhaps no, in which case sorry for the noise.

Best, Jean-François

------------------------------------------------------------------------

Emacs  : GNU Emacs 24.5.6 (x86_64-apple-darwin13.4.0, Carbon Version 157 AppKit 
1265.21)
 of 2015-08-26 on Atago.local
Package: 11.88.8

current state:
==============
(setq
 AUCTeX-date "2015-08-28"
 window-system 'mac
 LaTeX-version "2e"
 TeX-style-path '("~/.emacs.d/auctex"
                  "/Users/xxxxxxxx/.emacs.d/elpa/auctex-11.88.8/style"
                  "/Users/xxxxxxxx/.emacs.d/auctex/auto"
                  "/Users/xxxxxxxx/.emacs.d/auctex/style" "auto" "style")
 TeX-auto-save t
 TeX-parse-self t
 TeX-master t
 [...]
 )