Issue 48 demonstrates that we don't check delta status from within binary incr calls. I've written tests for both incr and decr to show the problem, but I don't have a way to report the error.
Currently, I'm using einval, but that's just kind of wrong since that's more to do with the input than the server-side state. Does anyone have any suggestions for better error reporting here? It's a bit of a corner case, but it would actually simplify things considerably as we currently have no easy way to provide varying response messages by error code type. What is definitely wrong is sending down EINVAL with "Invalid arguments" as the error message.
