* helm-mode.el: Allow exiting when predicate return non--nil (#707).
i.e exit when predicate returns non--nil even if must-match is t.
(helm-read-file-name,
helm-comp-read): Bind `minibuffer-completion-predicate'.
* helm.el (helm-confirm-and-exit-minibuffer): Test with `minibuffer-completion-predicate'.
* helm.el: Handle also predicate with two args for hash tables (#707).
(helm-confirm-and-exit-minibuffer): Do it.
* helm.mode.el (helm-comp-read): Bind minibuffer-completion-table.