Specifying spec level in session

I think it might be useful for local end language bindings to be able to
determine the level of the protocol being spoken by the remote end when a
session is created. To that end, it might be interesting to have the
specification level documented in the capabilities returned by the new
session command.

My proposal would be to add a "specificationLevel" entry to the set of
"server capabilities" listed in the "Processing Capabilities" algorithm of
section 4. A compliant remote end must set the value of this capability to
1 for remote ends adhering to the current version of the spec. When level 2
of the WebDriver spec is completed, compliant remote ends must set the
value to 2, and so on.

Thoughts?

--Jim