[Reviewer: Rob] Add support for protocol independent (IPv4/IPv6) table indices based upon RFC 4001.

I believe this is a way to move forward from the IpAddress table indices used in the current MIB. I'm not sure it is the best way. It is more of an experiment, and a place to start the discussion of how to proceed.
Looks like these changes are not backwards-compatible - users of the current version won't be able to use this MIB file - so we'd need some extra documentation here.