fixed cteate temporary field of subselect bug

mysql-test/r/subselect.result:
  test of cteate temporary field of subselect bug
mysql-test/t/subselect.test:
  test of cteate temporary field of subselect bug

mysql-test/r/subselect.result

 select (select 2);
 (select 2)
 2
+SELECT (SELECT 1) UNION SELECT (SELECT 2);
+(SELECT 1)
+1
+2
 drop table if exists t1,t2,t3,t4,t5,attend,clinic,inscrit;
 create table t1 (a int);
 create table t2 (a int, b int);

mysql-test/t/subselect.test

 
 select (select 2);
+SELECT (SELECT 1) UNION SELECT (SELECT 2);
 drop table if exists t1,t2,t3,t4,t5,attend,clinic,inscrit;
 create table t1 (a int);
 create table t2 (a int, b int);

sql/sql_select.cc

@@ -3605,6 +3605,7 @@ Field *create_tmp_field(THD *thd, TABLE *table,Item *item, Item::Type type,
   case Item::COND_ITEM:
   case Item::FIELD_AVG_ITEM:
   case Item::FIELD_STD_ITEM:
+  case Item::SUBSELECT_ITEM:
     /* The following can only happen with 'CREATE TABLE ... SELECT' */
   case Item::INT_ITEM:
   case Item::REAL_ITEM: