Performance improvements and fix release.

• Improvements
  • Check tend duration and compare it to tend interval, and warn the user if tend takes longer than tend interval.
  • Seed the cluster concurrently, and return as soon as any of the seeds is validated.
  • Tend the cluster concurrently. Allows use of very big clusters with no delay.
  • Partitions the connection queue to avoid contention.
  • Cluster partition map is merged from all node fragments and updated only once per tend to reduce contention to absolute minimum.
• Fixes
  • Fixed an issue where a valid but unreachable seed could timeout and stall connecting and tending the cluster.
  • Fix result code comments.