bug#7700: 24.0.50; C-y binding withing Isearch mode

[Juri Linkov]

> Thus, I propose two alternatives:
> a) In Isearch (forward or backward), every movement command would
> update the grabbed text. If the last grabbed text was in a different
> side of the point than current, switch the direction of the Isearch.
> b) The same, but replacing the direction switching with "exit Isearch
> mode and move point in the buffer".

ISTR this feature discussed on emacs-devel some time ago as
`isearch-selection-mode'.