SPARK-1203 fix saving to hdfs from yarn

Author: Thomas Graves <tgraves@apache.org>

Closes #173 from tgravescs/SPARK-1203 and squashes the following commits:

4fd5ded [Thomas Graves] adding import
964e3f7 [Thomas Graves] SPARK-1203 fix saving to hdfs from yarn

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

@@ -41,6 +41,7 @@ import org.apache.hadoop.mapreduce.lib.output.{FileOutputFormat => NewFileOutput
 import org.apache.hadoop.mapred.SparkHadoopWriter
 
 import org.apache.spark._
+import org.apache.spark.deploy.SparkHadoopUtil
 import org.apache.spark.Partitioner.defaultPartitioner
 import org.apache.spark.SparkContext._
 import org.apache.spark.partial.{BoundedDouble, PartialResult}
@@ -723,6 +724,7 @@ class PairRDDFunctions[K: ClassTag, V: ClassTag](self: RDD[(K, V)])
     if (valueClass == null) {
       throw new SparkException("Output value class not set")
     }
+    SparkHadoopUtil.get.addCredentials(conf)
 
     logDebug("Saving as hadoop file of type (" + keyClass.getSimpleName + ", " +
       valueClass.getSimpleName + ")")