Add BusyBird::SafeData.
Util: sort_statuses(): use SafeData to access status fields. Pass t/Util_sort_statuses.t
Util: split_with_entities(): use SafeData to access indices. Pass t/Util_split_with_entities.t
t/testlib/StatusStorage/CrazyStatus: add $opts param to test_storage_crazy_statuses() method. It's not used for now, though.
StatusStorage::Memory: put_statuses(): now it inspects the structures of the input statuses and croaks if it finds something wrong.