[SPARK-2529] Clean closures in foreach and foreachPartition.

Author: Reynold Xin <rxin@apache.org>

Closes #1583 from rxin/closureClean and squashes the following commits:

8982fe6 [Reynold Xin] [SPARK-2529] Clean closures in foreach and foreachPartition.

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

@@ -754,14 +754,16 @@ abstract class RDD[T: ClassTag](
    * Applies a function f to all elements of this RDD.
    */
   def foreach(f: T => Unit) {
-    sc.runJob(this, (iter: Iterator[T]) => iter.foreach(f))
+    val cleanF = sc.clean(f)
+    sc.runJob(this, (iter: Iterator[T]) => iter.foreach(cleanF))
   }
 
   /**
    * Applies a function f to each partition of this RDD.
    */
   def foreachPartition(f: Iterator[T] => Unit) {
-    sc.runJob(this, (iter: Iterator[T]) => f(iter))
+    val cleanF = sc.clean(f)
+    sc.runJob(this, (iter: Iterator[T]) => cleanF(iter))
   }
 
   /**