poll one lookupd endpoint per interval

* configurable jitter when polling lookupd (default now up to 30% of poll interval)
* set default lookupd poll interval to 60s
Merge pull request #39 from jehiah/distribute_lookupd_39

distribute lookupd requests
improve RDY handling for new connections

* occasionally choose a random connection for RDY when num conns > max_in_flight
* loop on a new connection when we're at RDY 0 and we cant send RDY non-0
Merge pull request #38 from jehiah/new_connections_38

RDY handling on new connections
update ChangeLog