fixed bug in sum function in subselect


mysql-test/r/subselect.result:
  subselect in having clause
mysql-test/t/subselect.test:
  subselect in having clause
sql/item.cc:
  subselect in having clause
sql/item.h:
  subselect in having clause
sql/item_cmpfunc.cc:
  subselect in having clause
sql/item_cmpfunc.h:
  subselect in having clause
sql/item_func.cc:
  subselect in having clause
sql/item_func.h:
  subselect in having clause
sql/item_strfunc.h:
  subselect in having clause
sql/item_subselect.cc:
  subselect in having clause
sql/item_subselect.h:
  subselect in having clause
sql/item_uniq.h:
  subselect in having clause
sql/sql_base.cc:
  subselect in having clause
sql/sql_class.cc:
  subselect in having clause
sql/sql_class.h:
  subselect in having clause
sql/sql_handler.cc:
  subselect in having clause
sql/sql_lex.cc:
  subselect in having clause
sql/sql_lex.h:
  subselect in having clause
sql/sql_prepare.cc:
  subselect in having clause
sql/sql_yacc.yy:
  subselect in having clause