Use protocol relative URL in ol.source.MapQuest
Use protocol relative URL in ol.source.Stamen
Save replay group, even if it is empty
Only replay replay group if it is not empty
Merge pull request #1695 from twpayne/fix-render-node-leak

Save replay group, even if empty
Merge pull request #1694 from twpayne/protocol-relative-url

Use protocol relative URL in tile sources
Add opacity property to ol.style.Image
Handle image opacity in ol.render.canvas.ImageReplay
Handle image opacity in ol.render.canvas.Immediate
Set ol.style.Icon opacity