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.
You're right---it does change the meaning of the name.  I think that, until we get all of the API functions merged, we don't want to try changing that name, because everyone will be using it as is, though.