bug#20419: 25.0.50; doc string of `recenter-last-op`

[Eli Zaretskii]

> Date: Sat, 25 Apr 2015 09:12:07 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: 20419-done@debbugs.gnu.org
> 
> > Yuck!  Why not set it to the first member of recenter-positions to
> > begin with?
> > 
> > FWIW, I consider this, including the exposure of this variable as
> > some kind of knob for other Lisp packages, bad style.  You should be
> > demanding cleaning this up instead of documenting it.
> > 
> > Fixed under protest.
> 
> Point taken.  A better design (for its use in `perform-replace')
> might bind `recenter-last-op' to the car of `recenter-positions'.

I'd rather suggest to have a simple function, recenter-reset-cycle,
say, and then hide its internals inside window.el.