scroll-backward with cursor-movement-scrolls=On

[Sergey Poznyakoff]

I have also fixed this:

> Now... just one more thing.  When cursor-movement-scrolls=On, the 
> action 'scroll-backward' should behave exactly the same way as
> when the cursor is on the top line and <up> is pressed.  So when 
> PageUp is bound to 'scroll-backward' and one is at the top of a 
> node, <PageUp> should not jump to the top of the preceding node, 
> but to its end.  So one can use <PageUp> and <PageDown> to quickly 
> skim through an entire document without missing a single paragraph.

Regards,
Sergey