[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

1 files changed, 5 insertions, 4 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
index 310d127506..b4c445b3ba 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
+++ b/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.