put back garbage collection with condition

src/bftsmart/clientsmanagement/ClientsManager.java

@@ -295,7 +295,7 @@ public class ClientsManager {
 
             if (ignore) {
                 
-                //Runtime.getRuntime().gc(); // force garbage collection
+                if(usedMemory <= this.controller.getStaticConf().getPreferredUsedMemory()) Runtime.getRuntime().gc(); // force garbage collection
 
                 logger.warn("Discarding message due to control flow mechanism\n" +
                         "\tMaximum requests are {}, current requests at {}\n" +