more efficient reference creation
fixed table_name of Field in temporary table


mysql-test/r/subselect.result:
  test of 2 references bugs
mysql-test/t/subselect.test:
  test of 2 references bugs
sql/field.h:
  fixed layout
  fixed table name of fields of temporary table (derived table)
sql/item.cc:
  more efficient reference creation
sql/sql_base.cc:
  fixed layout
  supported possiblity of item substitute (fixed bug)