fixed subselect error handling bug
fixed subselect UNION ALL bug
fixed thd->lex.select restoring
explain UNION subselect bug


mysql-test/r/subselect.result:
  test for:
    subselect UNION ALL bug
    subselect error handling bug
    explain UNION subselect bug
mysql-test/t/subselect.test:
  test for:
    subselect UNION ALL bug
    subselect error handling bug
    explain UNION subselect bug
sql/sql_lex.cc:
  fixed subselect UNION ALL bug
sql/sql_lex.h:
  fixed subselect UNION ALL bug
sql/sql_parse.cc:
  fixed subselect UNION ALL bug
sql/sql_select.cc:
  fixed subselect error handling bug
  fixed explain UNION subselect bug
sql/sql_union.cc:
  fixed thd->lex.select restoring
  code cleanup
  fixed subselect error handling bug
  fixed subselect UNION ALL bug
sql/sql_yacc.yy:
  fixed subselect UNION ALL bug