Merge pull request #112 from kayousterhout/ui_task_attempt_id

Display both task ID and task attempt ID in UI, and rename taskId to taskAttemptId

Previously only the task attempt ID was shown in the UI; this was confusing because the job can be shown as complete while there are tasks still running.  Showing the task ID in addition to the attempt ID makes it clear which tasks are redundant.

This commit also renames taskId to taskAttemptId in TaskInfo and in the local/cluster schedulers.  This identifier was used to uniquely identify attempts, not tasks, so the current naming was confusing.  The new naming is also more consistent with map reduce.

core/src/main/scala/org/apache/spark/ui/jobs/StagePage.scala

@@ -83,8 +83,8 @@ private[spark] class StagePage(parent: JobProgressUI) {
         </div>
 
       val taskHeaders: Seq[String] =
-        Seq("Task ID", "Status", "Locality Level", "Executor", "Launch Time", "Duration") ++
-        Seq("GC Time") ++
+        Seq("Task Index", "Task ID", "Status", "Locality Level", "Executor", "Launch Time") ++
+        Seq("Duration", "GC Time") ++
         {if (hasShuffleRead) Seq("Shuffle Read")  else Nil} ++
         {if (hasShuffleWrite) Seq("Write Time", "Shuffle Write") else Nil} ++
         Seq("Errors")
@@ -153,6 +153,7 @@ private[spark] class StagePage(parent: JobProgressUI) {
     val gcTime = metrics.map(m => m.jvmGCTime).getOrElse(0L)
 
     <tr>
+      <td>{info.index}</td>
       <td>{info.taskId}</td>
       <td>{info.status}</td>
       <td>{info.taskLocality}</td>