Refine signature of methods on Clients structure
Renamed Requests -> Replies, to more correctly match its contents.
Renamed Actions -> Requests, to reflect all the data they encompass.

It turns out the full information on the client request is necessary, not just the action.  Not changing the core RaftLogEntry yet, but peripheral code changed.
Fully integrated notion of client index.

Now the leader checks for old requests before appending them, failing repeated requests appended but not committed and succeeding those that have already been committed.