DBUG_ASSERT(fixed == 0) added to fix_fields()

sql/item.cc:
  layout fixed
  fixed bug in prepared statements with subqueries and outer references
sql/item.h:
  neg_transformer get thd argument to call fix_fields
sql/item_cmpfunc.cc:
  DBUG_ASSERT(fixed == 0) added to fix_fields()
  fixed Item_in_optimizer fixed flag
  neg_arguments(), neg_transformer() call fix_field() on created items to avoid bouble fix field or non-called fixfields()
sql/item_cmpfunc.h:
  neg_transformer get thd argument to call fix_fields
  fixed forgoten cleanup() call of parent class
sql/item_func.cc:
  DBUG_ASSERT(fixed == 0) and fixed flag check added to fix_fields()
sql/item_func.h:
  DBUG_ASSERT(fixed == 0) added to fix_fields()
  fixed forgoten cleanup() call of parent class
sql/item_row.cc:
  DBUG_ASSERT(fixed == 0) added to fix_fields()
  added forgoten 'fixed' flag set
sql/item_subselect.cc:
  DBUG_ASSERT(fixed == 0) added to fix_fields()
  fixed subquery transformation
sql/sql_base.cc:
  check of fixed flag added
sql/sql_derived.cc:
  fixed cleunup union in derived table during EXPLAIN command processing
sql/sql_select.cc:
  thd argument add to function to allow call fix_fields() of new created items
  fixed EXPLAIN double preparation
  check of fixed flag added
  eliminate_not_funcs fixed for corrcet fix_fields call of new created items
sql/sql_select.h:
  thd argument add to function to allow call fix_fields() of new created items
sql/sql_union.cc:
  union processing fixed
tests/client_test.c:
  layout fixed
  new test of outer references fron subqueries

sql/item_sum.h

@@ -533,6 +533,7 @@ public:
   const char *func_name() const { return udf.name(); }
   bool fix_fields(THD *thd, TABLE_LIST *tables, Item **ref)
   {
+    DBUG_ASSERT(fixed == 0);
     fixed= 1;
     return udf.fix_fields(thd,tables,this,this->arg_count,this->args);
   }