bug#14714: 24.3.50; `isearch-filter-predicate(s)'

[Stefan Monnier]

> 1. `isearch-filter-predicates' should not be an _alias_ for
> `isearch-filter-predicate'.  The former cannot just replace the latter.

Actually, shouldn't we revert this change and use
(add-function :before-while ...) on isearch-filter-predicate instead?
Admittedly, currently nadvice.el does not give you access to the list of
functions so you can't directly do the equivalent of

                   (mapconcat (lambda (s)
                                (and (symbolp s)
                                     (get s 'isearch-message-prefix)))
                              (if (consp isearch-filter-predicates)
                                  isearch-filter-predicates
                                (list isearch-filter-predicates))
                              "")

but that could be remedied (even using an advice's property rather than
a symbol property on the function added as advice).


        Stefan