[SPARK-5187][SQL] Fix caching of tables with HiveUDFs in the WHERE clause

Author: Michael Armbrust <michael@databricks.com>

Closes #3987 from marmbrus/hiveUdfCaching and squashes the following commits:

8bca2fa [Michael Armbrust] [SPARK-5187][SQL] Fix caching of tables with HiveUDFs in the WHERE clause

sql/hive/src/test/scala/org/apache/spark/sql/hive/CachedTableSuite.scala

@@ -158,4 +158,10 @@ class CachedTableSuite extends QueryTest {
     uncacheTable("src")
     assert(!isMaterialized(rddId), "Uncached in-memory table should have been unpersisted")
   }
+
+  test("CACHE TABLE with Hive UDF") {
+    sql("CACHE TABLE udfTest AS SELECT * FROM src WHERE floor(key) = 1")
+    assertCached(table("udfTest"))
+    uncacheTable("udfTest")
+  }
 }

sql/hive/v0.12.0/src/main/scala/org/apache/spark/sql/hive/Shim12.scala

@@ -44,7 +44,7 @@ import scala.language.implicitConversions
 
 import org.apache.spark.sql.catalyst.types.DecimalType
 
-class HiveFunctionWrapper(var functionClassName: String) extends java.io.Serializable {
+case class HiveFunctionWrapper(functionClassName: String) extends java.io.Serializable {
   // for Serialization
   def this() = this(null)
 

sql/hive/v0.13.1/src/main/scala/org/apache/spark/sql/hive/Shim13.scala

@@ -53,7 +53,7 @@ import scala.language.implicitConversions
  *
  * @param functionClassName UDF class name
  */
-class HiveFunctionWrapper(var functionClassName: String) extends java.io.Externalizable {
+case class HiveFunctionWrapper(var functionClassName: String) extends java.io.Externalizable {
   // for Serialization
   def this() = this(null)