bug#11378: 24.1.50; Suggestion: Let M-i in isearch cycle `search-invisible'

[Juri Linkov]

> There are more isearch filters that could share the same map `M-s f'.

Actually, currently these isearch filters can be used only one at a time.

It would be more useful to allow multiple filters by transforming
`isearch-filter-predicate' from the variable defining a predicate to the
hook-like list defining a set of predicates all of which should satisfy
for the search hit.

The default value could be a list with the current default element
`isearch-filter-visible'.  And it still could allow a symbol as its value
for backward compatibility.