[SPARK-5373][SQL] Literal in agg grouping expressions leads to incorrect result

`select key, count( * ) from src group by key, 1`  will get the wrong answer.

e.g. for this table
```
  val testData2 =
    TestSQLContext.sparkContext.parallelize(
      TestData2(1, 1) ::
      TestData2(1, 2) ::
      TestData2(2, 1) ::
      TestData2(2, 2) ::
      TestData2(3, 1) ::
      TestData2(3, 2) :: Nil, 2).toSchemaRDD
  testData2.registerTempTable("testData2")
```
result of `SELECT a, count(1) FROM testData2 GROUP BY a, 1`  is

```
                     [1,1]
                     [2,2]
                     [3,1]
```

Author: wangfei <wangfei1@huawei.com>

Closes #4169 from scwf/agg-bug and squashes the following commits:

05751db [wangfei] fix bugs when literal in agg grouping expressioons

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala

@@ -141,10 +141,11 @@ object PartialAggregation {
         // We need to pass all grouping expressions though so the grouping can happen a second
         // time. However some of them might be unnamed so we alias them allowing them to be
         // referenced in the second aggregation.
-        val namedGroupingExpressions: Map[Expression, NamedExpression] = groupingExpressions.map {
-          case n: NamedExpression => (n, n)
-          case other => (other, Alias(other, "PartialGroup")())
-        }.toMap
+        val namedGroupingExpressions: Map[Expression, NamedExpression] =
+          groupingExpressions.filter(!_.isInstanceOf[Literal]).map {
+            case n: NamedExpression => (n, n)
+            case other => (other, Alias(other, "PartialGroup")())
+          }.toMap
 
         // Replace aggregations with a new expression that computes the result from the already
         // computed partial evaluations and grouping values.

sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala

@@ -186,6 +186,15 @@ class SQLQuerySuite extends QueryTest with BeforeAndAfterAll {
       Seq(Row(1,3), Row(2,3), Row(3,3)))
   }
 
+  test("literal in agg grouping expressions") {
+    checkAnswer(
+      sql("SELECT a, count(1) FROM testData2 GROUP BY a, 1"),
+      Seq(Row(1,2), Row(2,2), Row(3,2)))
+    checkAnswer(
+      sql("SELECT a, count(2) FROM testData2 GROUP BY a, 2"),
+      Seq(Row(1,2), Row(2,2), Row(3,2)))
+  }
+
   test("aggregates with nulls") {
     checkAnswer(
       sql("SELECT MIN(a), MAX(a), AVG(a), SUM(a), COUNT(a) FROM nullInts"),