fixes & improvements
fixes & improvements

* just make b.N == num messages to process, this:
  - avoids the need to clear the structures
  - helps the bench runner reach a high b.N quickly
* nicer sequence of timestamps. fixes t=0 being dropped

raintank/metrictank,raintank/raintank-metric,replay/metrictank,replay/metrictank,raintank/metrictank,OOM-Killer/metrictank,OOM-Killer/metrictank,raintank/raintank-metric,replay/metrictank,raintank/metrictank,raintank/metrictank,replay/metrictank,OOM-Killer/metrictank,raintank/raintank-metric