this was true also for INSERT SELECT, UPDATE, DELETE. This fix will be removed when Maria supports COMMIT/ROLLBACK
("Maria 2.0"), because then Maria will trans_register_ha() and so participate in ha_commit_trans().
Without the fix, the assertion added to ha_maria::external_lock() fires many times in *maria*.test.

sql/sql_parse.cc:
  Before sending OK to client, commit transaction in Maria.
storage/maria/ha_maria.cc:
  Assertion added to external_lock() when committing: OK should not have been sent yet (ACI*D*).
  In ha_maria::implicit_commit(), possibility to not create a new transaction, this is used
  before net_end_statement(), when the next step is close_thread_tables();
  in this use case, ha_maria::implicit_commit() should not commit if under LOCK TABLES.
storage/maria/ha_maria.h:
  new prototype