Merge pull request #493 from kayousterhout/double_add

Fixed bug where task set managers are added to queue twice

@mateiz can you verify that this is a bug and wasn't intentional? (https://github.com/apache/incubator-spark/commit/90a04dab8d9a2a9a372cea7cdf46cc0fd0f2f76c#diff-7fa4f84a961750c374f2120ca70e96edR551)

This bug leads to a small performance hit because task
set managers will get offered each rejected resource
offer twice, but doesn't lead to any incorrect functionality.

Thanks to @hdc1112 for pointing this out.

core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala

@@ -592,7 +592,7 @@ private[spark] class TaskSetManager(
   override def removeSchedulable(schedulable: Schedulable) {}
 
   override def getSortedTaskSetQueue(): ArrayBuffer[TaskSetManager] = {
-    var sortedTaskSetQueue = ArrayBuffer[TaskSetManager](this)
+    var sortedTaskSetQueue = new ArrayBuffer[TaskSetManager]()
     sortedTaskSetQueue += this
     sortedTaskSetQueue
   }