* lisp/replace.el (replace-regexp-lax-whitespace): New defcustom.

* lisp/replace.el (replace-regexp-lax-whitespace): New defcustom.
(replace-lax-whitespace, query-replace-regexp)
(query-replace-regexp-eval, replace-regexp): Doc fix.
(perform-replace, replace-highlight): Let-bind
isearch-lax-whitespace to replace-lax-whitespace and
isearch-regexp-lax-whitespace to replace-regexp-lax-whitespace.

* lisp/isearch.el (isearch-query-replace): Let-bind
replace-lax-whitespace to isearch-lax-whitespace and
replace-regexp-lax-whitespace to
isearch-regexp-lax-whitespace.