Adaption for Sqlite

There are few issues in PR.

Sqlite does not support adding foreign keys on-the-fly, so `book.next_volume` must be already in SQL dump for `Table.self-reference.phpt`. It affects `Table.get().phpt`. Is there any reason to not declare this column in SQL dumps for all databases?

Sqlite does not support multi-inserts. Workaround exists:
```sql
INSERT INTO table (col, col) SELECT col, col UNION col, col
```
and this is what I'm working on, but let me know if it is not necessary.