I think they are from the Directory Opus 10 XP Icons set that Cris made.
I'm not totally happy with the blue or green icons on the darker blue background (and tighter margins) of the file display toolbar, but haven't got around to trying other alternatives. The green ones show up a bit better but I think the best thing may be just having arrows without the circles. I haven't tried that yet, though, so I don't know if it will work as well as I think.