Use Isearch lax whitespace mode in Info.

Use Isearch lax whitespace mode in Info.
http://lists.gnu.org/archive/html/emacs-devel/2012-08/msg00811.html

* lisp/info.el (Info-search): Don't check for isearch-mode and
isearch-regexp before let-binding search-spaces-regexp to
Info-search-whitespace-regexp.
(Info-isearch-search): Let-bind Info-search-whitespace-regexp to
search-whitespace-regexp if isearch-lax-whitespace or
isearch-regexp-lax-whitespace is non-nil.
(Info-mode): Don't set local variable search-whitespace-regexp.