bug#9706: 24.0.50; option to let prefix arg pass to command on isearch-mode-map

[Juri Linkov]

Version: 24.3.50

> See emacs-devel thread "`isearch-allow-scroll' - a misnomer and a bad
> design".  It was agreed to add an option to let C-u pass through to
> commands on isearch-mode-map.

This feature was implemented by Alan in
http://lists.gnu.org/archive/html/emacs-devel/2011-09/msg00216.html
and
http://lists.gnu.org/archive/html/emacs-devel/2013-06/msg00049.html