Add sets support in the console backend.

The backend dumps all values stored in all the buckets being sets.

This allows easy debugging by showing all values that are stored in
each bucket.

backends/console.js

@@ -34,6 +34,13 @@ ConsoleBackend.prototype.flush = function(timestamp, metrics) {
     counter: this.statsCache.counters,
     timers: this.statsCache.timers,
     gauges: metrics.gauges,
+    sets: function (vals) {
+      var ret = {};
+      for (val in vals) {
+        ret[val] = vals[val].values();
+      }
+      return ret;
+    }(metrics.sets),
     pctThreshold: metrics.pctThreshold
   };