* lisp/isearch.el (isearch-search-fun-default): New function.
(isearch-search-fun): Move default part to the new function
`isearch-search-fun-default'.
(isearch-search-fun-function): Set the default value to
`isearch-search-fun-default'.
* lisp/comint.el (comint-history-isearch-end):
Use `isearch-search-fun-default'.
(comint-history-isearch-search): Use `isearch-search-fun-default'
and remove spacial case for `isearch-word'.
(comint-history-isearch-wrap): Remove spacial case for
`isearch-word'.
* lisp/hexl.el (hexl-isearch-search-function):
Use `isearch-search-fun-default'.
* lisp/info.el (Info-isearch-search): Use `isearch-search-fun-default'.
Use `word-search-regexp' for `isearch-word'.
* lisp/misearch.el (multi-isearch-search-fun):
Use `isearch-search-fun-default'.
* lisp/simple.el (minibuffer-history-isearch-search):
Use `isearch-search-fun-default' and remove spacial case for
`isearch-word'.
(minibuffer-history-isearch-wrap): Remove spacial case for
`isearch-word'.
* lisp/textmodes/reftex-global.el (reftex-isearch-wrap-function):
Remove spacial case for `isearch-word'.
(reftex-isearch-isearch-search): Use `isearch-search-fun-default'.