*** Isearch can now temporarily show parts of the buffer which are<BR>
hidden by an overlay with a invisible property, when the search match
is inside that portion of the buffer.  To enable this the overlay
should have a isearch-open-invisible property which is a function that
would be called having the overlay as an argument, the function should
make the overlay visible.
<P>
During incremental search the overlays are shown by modifying the
invisible and intangible properties, if beside this more actions are
needed the overlay should have a isearch-open-invisible-temporary
which is a function. The function is called with 2 arguments: one is
the overlay and the second is nil when it should show the overlay and
t when it should hide it.
<P>