mysql-test/r/subselect_innodb.result:
  bug 2048 test
mysql-test/t/subselect_innodb.test:
  bug 2048 test
sql/item_subselect.cc:
  do not unlock tables for subqueries
sql/sql_derived.cc:
  derived table tables can be unlocked
sql/sql_lex.h:
  new interface to pass additional options
sql/sql_union.cc:
  new interface to pass additional options
  do not unlock tables for UNION