For obvious compatibility reasons, the over-the-wire protocol needs to be

versioned. Since we're using HTTP, it makes sense to simply version the

URLs used.

The scheme is pretty simple:

http://host:port/operation/version(/extra)?

where "version" is a simple integer.

Open questions:

- Are there operations where we don't want to require a version?

- Is there a use for a "300 Multiple Choices" HTTP return code?

- If we always try the client-optimal version first and then back off

linearly, we'll want to cache the version that succeeded so we don't

spend all of our time trying versions that don't exist.

- Alternatively, we can call "versions" to find out what versions the

server supports for each operation, and cache that.