SPARK-1628: Add missing hashCode methods in Partitioner subclasses

JIRA: https://issues.apache.org/jira/browse/SPARK-1628

Added `hashCode` in HashPartitioner, RangePartitioner, PythonPartitioner and PageRankUtils.CustomPartitioner.

Author: zsxwing <zsxwing@gmail.com>

Closes #549 from zsxwing/SPARK-1628 and squashes the following commits:

2620936 [zsxwing] SPARK-1628: Add missing hashCode methods in Partitioner subclasses

core/src/main/scala/org/apache/spark/Partitioner.scala

@@ -83,6 +83,8 @@ class HashPartitioner(partitions: Int) extends Partitioner {
     case _ =>
       false
   }
+
+  override def hashCode: Int = numPartitions
 }
 
 /**
@@ -119,7 +121,7 @@ class RangePartitioner[K : Ordering : ClassTag, V](
     }
   }
 
-  def numPartitions = partitions
+  def numPartitions = rangeBounds.length + 1
 
   private val binarySearch: ((Array[K], K) => Int) = CollectionsUtils.makeBinarySearch[K]
 
@@ -155,4 +157,17 @@ class RangePartitioner[K : Ordering : ClassTag, V](
     case _ =>
       false
   }
+
+
+  override def hashCode(): Int = {
+    val prime = 31
+    var result = 1
+    var i = 0
+    while (i < rangeBounds.length) {
+      result = prime * result + rangeBounds(i).hashCode
+      i += 1
+    }
+    result = prime * result + ascending.hashCode
+    result
+  }
 }

core/src/main/scala/org/apache/spark/api/python/PythonPartitioner.scala

@@ -50,4 +50,6 @@ private[spark] class PythonPartitioner(
     case _ =>
       false
   }
+
+  override def hashCode: Int = 31 * numPartitions + pyPartitionFunctionId.hashCode
 }

examples/src/main/scala/org/apache/spark/examples/bagel/PageRankUtils.scala

@@ -124,4 +124,6 @@ class CustomPartitioner(partitions: Int) extends Partitioner {
       c.numPartitions == numPartitions
     case _ => false
   }
+
+  override def hashCode: Int = numPartitions
 }