bug#956: In CVS Emacs, replace-regexp doesn't honor inhibit-read-only.

[Francis Litterio]

In CVS Emacs, replace-regexp doesn't honor inhibit-read-only.  To
reproduce, evaluate this form:

   (let ((inhibit-read-only t))
     (with-current-buffer (get-buffer-create "zzz")
       (insert "fooxxxbar")
       (replace-regexp "x+" "z" nil (point-min) (point-max))))

You will see this error: Buffer is read-only: #<buffer zzz>

This may be caused by this code in function perform-replace (in
lisp/replace.el):

   (let ((inhibit-read-only
          query-replace-skip-read-only))

The docstring for query-replace-skip-read-only says:

   *Non-nil means `query-replace' and friends ignore read-only matches.

which does not seem to match how it is used in that let form, especially
since replace-regexp is not interactive like query-replace.
--
Fran