Merge pull request #591 from mengxr/transient-new.

SPARK-1076: [Fix #578] add @transient to some vals

I'll try to be more careful next time.

Author: Xiangrui Meng <meng@databricks.com>

Closes #591 and squashes the following commits:

2b4f044 [Xiangrui Meng] add @transient to prev in ZippedWithIndexRDD add @transient to seed in PartitionwiseSampledRDD

core/src/main/scala/org/apache/spark/rdd/PartitionwiseSampledRDD.scala

@@ -45,7 +45,7 @@ class PartitionwiseSampledRDDPartition(val prev: Partition, val seed: Long)
 class PartitionwiseSampledRDD[T: ClassTag, U: ClassTag](
     prev: RDD[T],
     sampler: RandomSampler[T, U],
-    seed: Long = System.nanoTime)
+    @transient seed: Long = System.nanoTime)
   extends RDD[U](prev) {
 
   override def getPartitions: Array[Partition] = {

core/src/main/scala/org/apache/spark/rdd/ZippedWithIndexRDD.scala

@@ -37,7 +37,7 @@ class ZippedWithIndexRDDPartition(val prev: Partition, val startIndex: Long)
  * @tparam T parent RDD item type
  */
 private[spark]
-class ZippedWithIndexRDD[T: ClassTag](prev: RDD[T]) extends RDD[(T, Long)](prev) {
+class ZippedWithIndexRDD[T: ClassTag](@transient prev: RDD[T]) extends RDD[(T, Long)](prev) {
 
   override def getPartitions: Array[Partition] = {
     val n = prev.partitions.size