[SPARK-9305] Rename org.apache.spark.Row to Item.

It's a thing used in test cases, but named Row. Pretty annoying because everytime I search for Row, it shows up before the Spark SQL Row, which is what a developer wants most of the time.

Author: Reynold Xin <rxin@databricks.com>

Closes #7638 from rxin/remove-row and squashes the following commits:

aeda52d [Reynold Xin] [SPARK-9305] Rename org.apache.spark.Row to Item.

core/src/test/scala/org/apache/spark/PartitioningSuite.scala

@@ -91,13 +91,13 @@ class PartitioningSuite extends SparkFunSuite with SharedSparkContext with Priva
 
   test("RangePartitioner for keys that are not Comparable (but with Ordering)") {
     // Row does not extend Comparable, but has an implicit Ordering defined.
-    implicit object RowOrdering extends Ordering[Row] {
-      override def compare(x: Row, y: Row): Int = x.value - y.value
+    implicit object RowOrdering extends Ordering[Item] {
+      override def compare(x: Item, y: Item): Int = x.value - y.value
     }
 
-    val rdd = sc.parallelize(1 to 4500).map(x => (Row(x), Row(x)))
+    val rdd = sc.parallelize(1 to 4500).map(x => (Item(x), Item(x)))
     val partitioner = new RangePartitioner(1500, rdd)
-    partitioner.getPartition(Row(100))
+    partitioner.getPartition(Item(100))
   }
 
   test("RangPartitioner.sketch") {
@@ -252,4 +252,4 @@ class PartitioningSuite extends SparkFunSuite with SharedSparkContext with Priva
 }
 
 
-private sealed case class Row(value: Int)
+private sealed case class Item(value: Int)

sql/catalyst/src/test/scala/org/apache/spark/sql/RandomDataGenerator.scala

@@ -69,8 +69,7 @@ object RandomDataGenerator {
    * Returns a function which generates random values for the given [[DataType]], or `None` if no
    * random data generator is defined for that data type. The generated values will use an external
    * representation of the data type; for example, the random generator for [[DateType]] will return
-   * instances of [[java.sql.Date]] and the generator for [[StructType]] will return a
-   * [[org.apache.spark.Row]].
+   * instances of [[java.sql.Date]] and the generator for [[StructType]] will return a [[Row]].
    *
    * @param dataType the type to generate values for
    * @param nullable whether null values should be generated