MINOR: stats: report the number of idle connections for each server

This adds two extra fields to the stats, one for the current number of idle
connections and one for the configured limit. A tooltip link now appears on
the HTML page to show these values in front of the active connection values.

This should be backported to 2.0 and 1.9 as it's the only way to monitor
the idle connections behaviour.
2 files changed