* Fix BUG#19217 "dict_load_indexes() may read the delete-mark incorrectly".
 * Remove obsolete and unused variables from srv0srv.c.
 * Remove srv_sys->operational since it is unused.
 * Make thread_id parameter in os_thread_create() optional.
 * Add platform-specific os_thread_ret_t and OS_THREAD_DUMMY_RETURN,
   and convert thread start functions to use them.