bug#12253: Restore window start position

[martin rudalics]

> Martin writes in bug#12230:
>
>>> +    (set-window-start (selected-window) (nth 3 hist))))))
>> [...]
>>> +    (set-window-start (selected-window) ostart)))
>> [...]
>>> +    (set-window-start (selected-window) ostart)))
>> Are you sure you want to force start positions here?
[...]
> The second change in `Info-history-back' and in `Info-history-forward'
> is to keep the original window positions while navigating through
> the Info history backward and forward.  I think this has the same importance
> as keeping the original window positions while navigating buffers
> with `next-buffer' and `previous-buffer'.

I fully agree with you.  But I was curious whether setting the window
start position should be allowed to override any (goto-char opoint)
following or preceding it (just in case a window got resized during
navigation).

martin