new error handling
Item_ref bug fixed


include/mysql_com.h:
  new error handling
  query cache pointer description
mysql-test/r/distinct.result:
  new result's after Monty's bug fixing
mysql-test/r/subselect.result:
  subselect with union test
mysql-test/t/subselect.test:
  subselect with union test
sql/item.cc:
  subselect with union
  Item_ref bug fixed
sql/item_cmpfunc.cc:
  Monty's bug fixing
sql/item_subselect.cc:
  TODO changing
  subselect with union
sql/item_subselect.h:
  subselect with union
sql/mysql_priv.h:
  Item_ref bug fixed
sql/mysqld.cc:
  new error handling
sql/net_pkg.cc:
  new error handling
sql/net_serv.cc:
  new error handling
sql/sql_base.cc:
  Item_ref bug fixed
sql/sql_class.cc:
  new error handling
sql/sql_class.h:
  new error handling
sql/sql_derived.cc:
  subselect with union
sql/sql_insert.cc:
  new error handling (only with mysql_select now)
sql/sql_lex.cc:
  subselect with union
sql/sql_lex.h:
  subselect with union
sql/sql_parse.cc:
  new error handling
sql/sql_select.cc:
  new error handling
  subselect with union
  removed thd->where=0 hack
sql/sql_select.h:
  subselect with union
sql/sql_union.cc:
  subselect with union
sql/sql_update.cc:
  new error handling (only with mysql_select now)
sql/sql_yacc.yy:
  subselect with union