[Poshuku] Removed obsolete warning.
[Poshuku] Moved history stuff to poshukutypes.h.
[Poshuku] StorageBackend::Create(void).
[Poshuku] Added IStorageBackend interface.
[Poshuku] Use StorageBackend::Create().

And don't do double Prepare().
[Poshuku] IProxyObject::CreateStorageBackend().