- latency measurements under 2 second intervals now operate in "continuous"
  mode: a single "ping" process runs per destination, versus the "normal"
  approach of forking a new fping process for each measurement instance.

- Note, that I found a bug which is not fixed in this checkin: if a latency
  test is running in continuous mode and another latency measurement request
  is received with a shorter interval, the "continuous" ping process is not
  re-initialized with the new, shorter interval.