NING-13292: NING-1329: Adding some tests for the counter event aggregator to ensure that the component is threadsafe and performant in scenarios where a single counter is aggregated rapidly and many counters are aggregated rapidly.  These tests have all been successful, and I declare this component ready for consumption.
Merge branch 'collector-metrics' of https://github.com/ning/collector into collector-metrics
NING-13292: NING-1329: Fixing one edge condition wherein flushing the buffer while counters are very active can cause undefined behavior.  The fix was to add some reference counting to the map being used in each aggregation.  This has had no measurable impact on performance, and the added test for this exposed error condition ensures that the flsuhing can be done in rapid succession without introducing errors to counters