* helm.el (helm-search-from-candidate-buffer): Allow using `filter-one-by-one' in candidates-in-buffer sources.
* helm-regexp.el (helm-source-buffers-list): Use now `filter-one-by-one'.
* helm.el (helm--maybe-process-filter-one-by-one-candidate): New macro.
(helm-search-from-candidate-buffer,
helm-match-from-candidates): Use it.
* helm.el (helm-match-from-candidates): No need to check cand in hash as it had been maybe modified by one-by-one filter.
* helm-regexp.el: Align let.
* helm.el (helm-output-filter--collect-candidates): Handle `filter-one-by-one', take one more arg 'source'.
* helm-grep.el (helm-do-grep-1): Use now filter-one-by-one.