Avoid too much cleaning of eventSets

We don't need to clean the eventSets if we used the same set at the
previous Spec

core/src/main/kotlin/se/lth/cs/papicounters/PapiTracerRunner.kt

@@ -93,17 +93,23 @@ open class PapiTracerRunner() : PapiRunner() {
         return g
     }
 
+    private var lastCountersUsed : List<PAPICounter>? = null
+
     fun runIterations(spec : PapiBenchmarkAnalyzer.RunSpec) : List<List<TraceRecord>> {
-        val counters = spec.counters()
-            .filter { ! it.isSpecial() } // These are active by default.
-            .map { it.toPAPIConstant()!! }
 
-        Tracer.clearCounters();
         Tracer.reset()
         Tracer.isTracing = true
 
-        for (c in counters) {
-            Tracer.addCounter(c)
+        if (spec.counters() != lastCountersUsed) {
+            System.err.println("Counters changed: (${spec.counters()} /vs/ $lastCountersUsed), cleaning")
+            val counters = spec.counters()
+                .filter { ! it.isSpecial() } // These are active by default.
+                .map { it.toPAPIConstant()!! }
+            Tracer.clearCounters();
+            for (c in counters) {
+                Tracer.addCounter(c)
+            }
+            lastCountersUsed = spec.counters()
         }
 
         val rangeIterations = 0 until spec.numberRuns