* [DEV-222] Changed type of TxOut.Value and util.Amount to uin64
* [DEV-222] Replaced math.MaxUint64 with 0
* [DEV-222] Fixed comment to reflect uint64 instead of int64
* [DEV-222] Fixed overflow comment
* [DEV-97] Moved github.com/daglabs/btcutil into github.com/daglabs/btcd/btcutil.
* [DEV-97] Updated Gopkg.toml to no longer refer to btcutil.
* [DEV-97] Renamed btcutil to util.
Rollback takes a block hash rather than a BlockStamp.
Increase rounds in TestEstimateFeeRollback to test dropping txs that have been in the mempool too long.