range: switch secondary and middle button on steppers

range: switch secondary and middle button on steppers

Clicking on steppers does different things depending on which
button you use. We used to scroll to the end on secondary click
and use high-speed autoscrolling on middle-click. Switch these
two around, since the scroll-to-end functionality is less likely
to be useful, and the seconary button makes the autoscrolling
more easily available.