[Fix #204] Update out-dated comments

This PR is self-explanatory.

Author: Andrew Or <andrewor14@gmail.com>

Closes #381 from andrewor14/master and squashes the following commits:

3e8dde2 [Andrew Or] Fix comments for #204

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -1191,11 +1191,7 @@ class SparkContext(config: SparkConf) extends Logging {
     listenerBus.post(SparkListenerApplicationStart(appName, startTime, sparkUser))
   }
 
-  /**
-   * Post the application end event to all listeners immediately, rather than adding it
-   * to the event queue for it to be asynchronously processed eventually. Otherwise, a race
-   * condition exists in which the listeners may stop before this event has been propagated.
-   */
+  /** Post the application end event */
   private def postApplicationEnd() {
     listenerBus.post(SparkListenerApplicationEnd(System.currentTimeMillis))
   }

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

@@ -31,8 +31,8 @@ import org.apache.spark.util.JsonProtocol
 /**
  * A SparkListenerBus that replays logged events from persisted storage.
  *
- * This class expects files to be appropriately prefixed as specified in EventLoggingListener.
- * There exists a one-to-one mapping between ReplayListenerBus and event logging applications.
+ * This assumes the given paths are valid log files, where each line can be deserialized into
+ * exactly one SparkListenerEvent.
  */
 private[spark] class ReplayListenerBus(
     logPaths: Seq[Path],