* lisp/isearch.el (isearch-mode-map): Bind `isearch-toggle-invisible' to "\M-si".

* lisp/isearch.el (isearch-mode-map): Bind `isearch-toggle-invisible' to "\M-si".
(isearch-invisible): New variable.
(isearch-forward): Doc fix.
(isearch-mode): Set `isearch-invisible'
to the value of `search-invisible'.
(isearch-toggle-case-fold): Doc fix.
(isearch-toggle-invisible): New command.
(isearch-query-replace): Let-bind `search-invisible'
to the value of `isearch-invisible'.
(isearch-search): Use `isearch-invisible' instead of
`search-invisible'.  Let-bind `search-invisible'
to the value of `isearch-invisible'.