Overlapping lines hidden when selecting legend

[AaronLS]

If you have a "Line Chart" graph with multiple overlapping lines, and click an item in the Legend to highlight a particular line, you may not see the line through other lines. The other lines get "greyed" but are still rendered over the would-be highlighted line. Same goes for the "points" rendered along the line. Essentially the highlighted line should probably be brought forward in the z order, or it's width increased so it shows from behind the other lines.