set scroll interval

[lmueller74]

when clicking on the scrollbar area (not dragging the bar itself), a normal scrollbar will almost center itself on the point clicked. this solution only scrolls a small amount, and the scrollbar does not focus to the point clicked on the scrollbar area.

it would be nice to have this work more like the native browser scrollbar implementation.

also - same behavior when using the scroll wheel on a mouse....maybe add a way to change the page size for each click of the scroll wheel?