revise the comments

Author: CodingCat

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

@@ -721,7 +721,7 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
       outputFormatClass: Class[_ <: NewOutputFormat[_, _]],
       conf: Configuration = self.context.hadoopConfiguration)
   {
-    // keep the source-compatibility and distinct with the SparkConf
+    // Rename this as hadoopConf internally to avoid shadowing (see SPARK-2038).
     val hadoopConf = conf
     val job = new NewAPIHadoopJob(hadoopConf)
     job.setOutputKeyClass(keyClass)
@@ -756,7 +756,7 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
       outputFormatClass: Class[_ <: OutputFormat[_, _]],
       conf: JobConf = new JobConf(self.context.hadoopConfiguration),
       codec: Option[Class[_ <: CompressionCodec]] = None) {
-    // keep the source-compatibility and distinct with the SparkConf
+    // Rename this as hadoopConf internally to avoid shadowing (see SPARK-2038).
     val hadoopConf = conf
     hadoopConf.setOutputKeyClass(keyClass)
     hadoopConf.setOutputValueClass(valueClass)
@@ -784,7 +784,7 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
    * configured for a Hadoop MapReduce job.
    */
   def saveAsNewAPIHadoopDataset(conf: Configuration) {
-    // keep the source-compatibility and distinct with the SparkConf
+    // Rename this as hadoopConf internally to avoid shadowing (see SPARK-2038).
     val hadoopConf = conf
     val job = new NewAPIHadoopJob(hadoopConf)
     val formatter = new SimpleDateFormat("yyyyMMddHHmm")
@@ -844,7 +844,7 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
    * MapReduce job.
    */
   def saveAsHadoopDataset(conf: JobConf) {
-    // keep the source-compatibility and distinct with the SparkConf
+    // Rename this as hadoopConf internally to avoid shadowing (see SPARK-2038).
     val hadoopConf = conf
     val outputFormatInstance = hadoopConf.getOutputFormat
     val keyClass = hadoopConf.getOutputKeyClass