[MERGE] Better infrastructure for tracking remote server version in SmartClientMedium

[Martin Pool]

Martin Pool has voted resubmit.
Status is now: Resubmit
Comment:
> .... keep
 > adding _remote_is_at_least_1_6 and trying to keep them all consistent 
with each

That's a noble goal.

However I feel like this is getting the same kind of problem with regard 
to the operators applied to these formats: !=, >=, etc are all being 
spelled out as words and it's not clear to me that they will always be 
consistent; or at least there seems a fair risk that they will become 
inconsistent with future evolution.

If we want to have an api that says what the remote version is I'd 
rather just expose the actual version tuple, or at least the approximate 
version tuple.

But more broadly, I thought our approach was that we wanted to avoid 
having the client making decisions based on the server version, because 
it's problematic with stateless http and seems to require a startup 
roundtrip which we wanted to avoid.  Maybe we want to reconsider it? 
But if it's just that we know the server doesn't support a particular 
operation or encoding, maybe we should record that fact specifically?

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20080604230505.GA1318%40steerpike.home.puzzling.org%3E