Fixes:
- Bug #18077: InnoDB uses full explicit table locks in stored FUNCTION


sql/ha_innodb.cc:
  Apply InnoDB snapshot ss923
  
  Revision r922:
  ha_innobase::store_lock(): When downgrading table locks, do not
  check thd->in_lock_tables but test if
  thd->lex->sql_command == SQLCOM_LOCK_TABLES
  instead.  Otherwise, stored functions will use table locks.  (Bug #18077)