Allow options per hasher class for Fallback.

This will be most useful for people upgrading and using different hash algos as the default sha1 or need to pass options for specific hashers in general.
If it was anything else it would trip right afterwards where it accesses it as an array. This is also just copy and paste from the other existing source - see the discussion above. So then we would need to change both. And I think the current way of checking should suffice.