Fixed bug #27229: crash when a set function aggregated in outer

context was used as an argument of GROUP_CONCAT.
Ensured correct setting of the depended_from field in references
generated for set functions aggregated in outer selects.
A wrong value of this field resulted in wrong maps returned by 
used_tables() for these references.
Made sure that a temporary table field is added for any set function
aggregated in outer context when creation of a temporary table is 
needed to execute the inner subquery. 


mysql-test/r/subselect.result:
  Added a test case for bug #27229.
mysql-test/t/subselect.test:
  Added a test case for bug #27229.
sql/item.cc:
  Fixed bug #27229: crash when a set function aggregated in outer
  context was used as an argument of GROUP_CONCAT.
  Ensured correct setting of the depended_from field in references
  generated for set functions aggregated in outer selects.
sql/item_sum.cc:
  Fixed bug #27229: crash when a set function aggregated in outer
  context was used as an argument of GROUP_CONCAT.
  Added the field aggr_sel to the objects of the class Item_sum.
  In any Item_sum object created for a set function this field 
  has to contain a pointer to the select where the set function
  is aggregated.
sql/item_sum.h:
  Fixed bug #27229: crash when a set function aggregated in outer
  context was used as an argument of GROUP_CONCAT.
  Added the field aggr_sel to the objects of the class Item_sum.
  In any Item_sum object created for a set function this field 
  has to contain a pointer to the select where the set function
  is aggregated.
  Added a method that says whether a set function is aggregated
  in outer context and, if so, returns the aggregating select.
  Removed the field nest_level_tables_count introduced by the
  patch for bug 24484 as aggr_sel->join->tables contains the
  sane number.
sql/sql_base.cc:
  Fixed bug #27229: crash when a set function aggregated in outer
  context was used as an argument of GROUP_CONCAT.
  Added the field aggr_sel to the objects of the class Item_sum.
  Removed changes introduced by the patch for bug 24484 as 
  the field leaf_count of the THD class is not used anymore.
sql/sql_class.h:
  Fixed bug #27229: crash when a set function aggregated in outer
  context was used as an argument of GROUP_CONCAT.
  Added the field aggr_sel to the objects of the class Item_sum.
  Removed changes introduce by the patch for bug 24484 as 
  the field leaf_count of the THD class is not used anymore.
sql/sql_insert.cc:
  Fixed bug #27229: crash when a set function aggregated in outer
  context was used as an argument of GROUP_CONCAT.
  Added the field aggr_sel to the objects of the class Item_sum.
  Removed changes introduce by the patch for bug 24484 as 
  the field leaf_count of the THD class is not used anymore.
sql/sql_select.cc:
  Fixed bug #27229: crash when a set function aggregated in outer
  context was used as an argument of GROUP_CONCAT.
  When creating a temporary table a field is added in it for any 
  set function aggregated in outer context.

sql/sql_base.cc

@@ -4864,7 +4864,6 @@ bool setup_tables_and_check_access(THD *thd,
   TABLE_LIST *leaves_tmp = NULL;
   bool first_table= true;
 
-  thd->leaf_count= 0;
   if (setup_tables (thd, context, from_clause, tables, conds, 
                     &leaves_tmp, select_insert))
     return TRUE;
@@ -4882,7 +4881,6 @@ bool setup_tables_and_check_access(THD *thd,
       return TRUE;
     }
     first_table= false;
-    thd->leaf_count++;
   }
   return FALSE;
 }