Generalize 'object_url' to take extra arguments

I used *args so that it would be backwards-compatible with previous usage.
The only difference, and it's minor, is that now all arguments are
urllib-quoted.  Tested with two- and three- argument calls.
This changes the semantics a bit; I chose the name `object_url` because I had been thinking of it in terms of "the group `foo` is located at `http://host:port/group/foo`, and we invoke methods off of that. now it's just gluing the endpoint to the front of a series of path segments. That's fine, but if we're going for that I'm not sure the name makes sense anymore.