bug#18923: Alternative scrolling model

[E Sabof]

Eli Zaretskii <eliz@gnu.org> writes:

> The current implementation only uses vscroll for partially visible
> screen lines (a.k.a. "glyph rows").  This is by design (and consistent
> with what line-move does), but we can decide to change that, if that's
> what people want.

Potentially I could try calling Lisp functions from window_scroll_pixel_based, 
until everything seemed to work. At which point the additional Lisp could be 
translated to C.

Evgeni