WL#1972 "Evaluate HAVING before SELECT select-list"

- post-review fix regarding Item_fields
- added test for the changed name resolution


mysql-test/r/having.result:
  Test for changed name resolution of Item_fields
mysql-test/t/having.test:
  Test for changed name resolution of Item_fields
sql/item.cc:
  - Changed Item_field::fix_fields to perform the same name
    resolution as Item_ref::fix_fields because column references
    of subqueries inside HAVING may be represented as Item_fields,
    and they need to be resolved as Item_refs.
  - Adjusted Item_field::fix_fields so that it has the same variable
    names and structure as Item_ref::fix_fields.

mysql-test/r/having.result

@@ -245,6 +245,13 @@ col1
 10
 10
 10
+select sum(col1) from t1
+group by col_t1
+having (select col_t1 from t2 where col_t1 = col_t2 order by col_t2 limit 1);
+sum(col1)
+40
+20
+30
 select t1.col1 from t1
 where t1.col2 in 
 (select t2.col2 from t2 

mysql-test/t/having.test

@@ -211,6 +211,11 @@ where t1.col2 in
       (select t2.col2 from t2 
        group by t2.col1, t2.col2 having col_t1 <= 10);
 
+# Item_field must be resolved in the same way as Item_ref
+select sum(col1) from t1
+group by col_t1
+having (select col_t1 from t2 where col_t1 = col_t2 order by col_t2 limit 1);
+
 # nested queries with HAVING, inner having column resolved in outer FROM clause
 # the outer having column is not referenced in GROUP BY which results in an error
 --error 1054
@@ -256,7 +261,6 @@ group by col_t1
 having col_t1 in (select sum(t2.col1) from t2
                   group by t2.col2, t2.col1 having t2.col1 = col_t1);
 
-
 #
 # queries with joins and ambiguous column names
 #