bug#12106: 24.1; be able to prevent `help-make-xrefs' from creating a cross ref

I would like some easy way to prevent `help-make-xrefs' from turning a
given `...' into a cross reference (link).

If I want to refer to a function or whatever without linking to
what Emacs thinks is the proper doc for it, what can I do?  The
current handling of `...' is too black-and-white.  There should
be some way to turn off link a particular instance of `...'.

E.g., we should be able to put something in the doc string that
(a) is not, itself, displayed and (b) prevents `help-make-xrefs'
from creating a link for that `...' occurrence.

If we did not care about making the indication invisible then it
might be enough to change, say, `help-xref-symbol-regexp' to this:

"\\(\\<\\(\\(variable\\|option\\)\\|\\(function\\|command\\)\\|\
\\(face\\)\\|\\(symbol\\|program\\|property\\)\\|\
\\(source \\(?:code \\)?\\(?:of\\|for\\)\\)\\)[  \n]+\\)?\
[^\\]`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'"
^^^^^
I.e., just let a backslash escape `...' from linking.  But that
puts a `\' in the output buffer as well.  (Perhaps it could be
made invisible?)

Anyway, I am not proposing the solution, I'm just filing the
enhancement request.

In GNU Emacs 24.1.1 (i386-mingw-nt5.1.2600)
 of 2012-06-10 on MARVIN
Windowing system distributor `Microsoft Corp.', version 5.1.2600