(fixed BUG#943)


mysql-test/r/subselect.result:
  test for bug 943
mysql-test/t/subselect.test:
  test for bug 943
sql/item.cc:
  bool field changed with enum
  prevented finding references in item_list for non-SELECT st_select_lex
sql/sql_lex.cc:
  bool field changed with enum
sql/sql_lex.h:
  bool field changed with enum
sql/sql_parse.cc:
  all subqueries and UNION parts marked as SELECT
sql/sql_yacc.yy:
  bool field changed with enum
  PRIMARY SELECT command st_select_lex marked as SELECT