fixed bug of calling setup_fields without correct lex->current_select pointer in mysql_derived
more correct creation of reference in Item_field::fix_field


mysql-test/r/subselect.result:
  new explain with subselect reduced
mysql-test/t/subselect.test:
  new explain with subselect reduced
sql/item.cc:
  support of subselect without FROM reducing
  more correct creation of reference in Item_field::fix_field
sql/item.h:
  support of subselect without FROM reducing
sql/item_cmpfunc.cc:
  support of subselect without FROM reducing
sql/item_cmpfunc.h:
  support of subselect without FROM reducing
sql/item_func.cc:
  support of subselect without FROM reducing
sql/item_func.h:
  support of subselect without FROM reducing
sql/item_row.cc:
  support of subselect without FROM reducing
sql/item_row.h:
  support of subselect without FROM reducing
sql/item_strfunc.h:
  fixed layout
  support of subselect without FROM reducing
sql/item_subselect.cc:
  support of subselect without FROM reducing
sql/item_subselect.h:
  support of subselect without FROM reducing
sql/mysql_priv.h:
  reference in Item_field::fix_field related changes
sql/sql_base.cc:
  reference in Item_field::fix_field related changes
sql/sql_derived.cc:
  fixed bug of calling setup_fields without correct lex->current_select pointer