Function libpijul::fs::get_latest_touch

pub fn get_latest_touch<'a, T: ChannelTxnT + DepsTxnT<DepsError = <T as GraphTxnT>::GraphError>>(
    txn: &T, 
    channel: &T::Channel, 
    pos: &Position<ChangeId>
) -> Result<(u64, ChangeId), TxnErr<T::GraphError>>