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

[Juri Linkov]

> As has often been the case, we think similarly (but differently too) here.
> In my previous msg I mentioned a different way to combine both possibilities
> (1: start with default vs 2: start from last)).  Not limited to Isearch,
> and togglable between the two start-with behaviors.

Since a separate user option is necessary anyway, currently
I'm preparing a patch that adds it to customize the behavior of
case-fold and invisible.  Based on that, later you could provide
a prefix arg to toggle this user option, if you wish.