bug#16493: 24.3.50; (setq search-invisible t) is useless, let's allow to turn visible-mode temporarily on

[Stefan Monnier]

> The difference (or lack thereof) between t and (t)

There is a rather large difference between the two.

> is something that's confusing, and should be preferably avoided.

Agreed and the way to avoid it, IMO, is to eliminate the `t` case which
is the weird one out whose behavior you can't rely on since some
other package may come around and call
(remove-from|add-to)-invisibility-spec from under you.


        Stefan