* lisp/isearch.el (isearch-search-fun-in-noncontiguous-region): New function.

* lisp/isearch.el (isearch-search-fun-in-noncontiguous-region): New function.

(isearch-search-fun-in-text-property): Refactor body to
'search-within-boundaries', then call it (bug#14013).
(search-within-boundaries): New function refactored from
isearch-search-fun-in-text-property.

* test/lisp/isearch-tests.el: Add tests for new search functions.
(isearch--test-search-within-boundaries): New function.
(isearch--test-search-fun-in-text-property)
(isearch--test-search-fun-in-noncontiguous-region): New tests.