Problem:
Aggregation does not happen correctly because substitution for
subquery is created with wrong item.

Analysis:
Currently while creating a substitution for ALL/ANY subqueries,
optimizer uses "real_item" instead of the ref_item.
If this happens to be a reference to an aggregate function
then it would be creating the substitution with SUM_FUNC_ITEM
rather than the REF_ITEM.

If an aggregate function is present in having clause, optimizer
calls split_sum_func2 to add the aggregate functions
to the list of items in the select list.

Ex: In the following query
select f1, sum(f2) as sum from t1 group by f1 having sum >
                                              all (select 1);

"sum" in having clause is a reference to sum(f2). So while
creating the substitution we create using the real_item of
"sum" which is sum(f2). In split_sum_func2 we add this
"sum(f2)" to the item list. As a result the item list now
becomes "sum(f2), f1, sum(f2)". This results in creation
of three fields in tmp_table. But both the sum(f2)'s would
be pointing to the same result_field. So, while aggregating
same result is added twice.
Before the fix for Bug#16095534, the type would remain
REF_ITEM and thereby optimizer would not be adding "sum"
to the select item list.

Solution:
The problem addressed in Bug#16095534 exists only for Item_ref
objects created while resolving not for the ref objects created
during parsing. So use real_item only for such items.