Attempt to ensure metric names are always unique

Only unique metric names will appear in New Relic, so text is added to
the metric name to ensure that all reported metrics have unique names.

newrelic_perfmon_plugin/Agent.cs

@@ -52,6 +52,7 @@ public override void PollCycle()
             try
             {
                 Scope.Connect();            
+                var metricNames = new Dictionary<string, int>();
 
                 foreach (Dictionary<string, Object> counter in Counters)
                 {
@@ -89,6 +90,15 @@ public override void PollCycle()
 
                                 string metricName = string.Format("{0}{2}/{1}", categoryName, counterName, instanceName);
 
+                                if (metricNames.ContainsKey(metricName))
+                                {
+                                    metricName = metricName + "#" + metricNames[metricName]++;
+                                }
+                                else
+                                {
+                                    metricNames.Add(metricName, 1);
+                                }
+
                                 logger.Debug("{0}/{1}: {2} {3}", Name, metricName, value, unitValue);
 
                                 ReportMetric(metricName, unitValue, value);