Add measure for latency to server sessions.

Measure is the time lapse from the receipt of the SERVERKEEPALIVE
and the SERVERSHAKE.  The result is stored as a rounded integer
representing millisecond lapse between those events.
Add client cache mechanism to avoid duplicate responses

Each client, by ip, is given a discrete list of servers for
its request.  This is generated on LISTREQ index 0 requests, so
that all subsequent non-zero index requests will have the same
list (in both size and composition).  Additional tests and config
were added to go with it.