Fixes T7069. When jumping to a comment anchor, we get the scroll positions wrong.

Partly this is fixing some calcaulations; partly, the "show older comments" and "scroll anchor" stuff were fighting over the scroll position. Since the anchor can take care of things on its own, just let it handle stuff.

• Clicked comment anchors.
• Loaded pages with anchors in the URI.
• Loaded pages with anchors hidden behind "show older comments".

In all cases, got the right scroll position.