bug#34038: 26.1; set-window-start sometimes fails to set window start

[Drew Adams]

> > Is there a way to reliably set the window-start in such situations?
> 
> I think this happens because you call set-window-start with last
> argument non-nil.  Doing that tells the display engine that the
> window-start point is just a suggestion, not a hard requirement.

Sorry for jumping in here ignorantly.  I just looked
at the doc string for `set-window-start' and got a
very different impression of what that 3rd arg means.
Am I mistaken?  How to reconcile your description
with what the doc string says?

  Optional third arg NOFORCE non-nil inhibits next
  redisplay from overriding motion of point in order
  to display at this exact start.