Add pseudo-timers for new_measure counts in location updates, close #220
Merge remote-tracking branch 'graydon/bug-220-location-update-metrics'
Change `check_stats` test helper to check for exact metric names.

Before we used prefix matches, to minimize the changes compared to the
older heka message checks. For those the metric name was only something
like `http.request` and not the full `http.request.v1.search.200`.
Convert new_measures metrics to proper gauges.