add non-chord keys to repeat isearch

["Drew Adams" <drew.adams@oracle.com>]

I often repeat `C-s' (same search string), over and over and over.
You too, right?  Poor pinky.

(define-key isearch-mode-map [next]  'isearch-repeat-forward)
(define-key isearch-mode-map [prior] 'isearch-repeat-backward)

Duh! Why I never bothered to do that before, I dunno. I've been doing it forever
in Framemaker (which doesn't have incremental search), but I never thought to do
it for Emacs too. Blinded by habit, I guess.

I propose that Emacs do the same thing out of the box.

Someone (Richard?) will no doubt argue that he prefers to have `next' exit
Isearch and move down a page, and similarly for alternative bindings one might
propose here. And perhaps there will be other arguments against (I know some
people just don't like adding bindings to `isearch-mode-map'). But to me this is
a no-brainer (now that I think of it ;-)).

WDOT?

P.S. No removal of any bindings, just addition of these two.
You can still use `C-s C-s C-s C-s C-s C-s' if you prefer.