[Spark 1877] ClassNotFoundException when loading RDD with serialized objects

Updated version of #821

Author: Tathagata Das <tathagata.das1565@gmail.com>
Author: Ghidireac <bogdang@u448a5b0a73d45358d94a.ant.amazon.com>

Closes #835 from tdas/SPARK-1877 and squashes the following commits:

f346f71 [Tathagata Das] Addressed Patrick's comments.
fee0c5d [Ghidireac] SPARK-1877: ClassNotFoundException when loading RDD with serialized objects

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

@@ -718,7 +718,7 @@ class SparkContext(config: SparkConf) extends Logging {
       minPartitions: Int = defaultMinPartitions
       ): RDD[T] = {
     sequenceFile(path, classOf[NullWritable], classOf[BytesWritable], minPartitions)
-      .flatMap(x => Utils.deserialize[Array[T]](x._2.getBytes))
+      .flatMap(x => Utils.deserialize[Array[T]](x._2.getBytes, Utils.getContextOrSparkClassLoader))
   }
 
   protected[spark] def checkpointFile[T: ClassTag](