* Add an OrderedUtxo type for validation of spends within a block
This change allows us to check that transparent spends use outputs from
earlier in their block. (But we don't actually do that check yet.)
We need to keep the order of UTXOs when we're contextually verifying
each new block that is added to a chain. But the block order is
irrelevant for UTXOs stored in the state.
* Take ownership in utxos_from_ordered_utxos
* Delete a confusing comment
bfc3e4a46c