Make RedeemData to sort keys.

So that these keys are stored in the same order they appear in redeem script. That would make easier for signers to locate signature position in scriptSig.
HDW: Create/activate a new HD chain when a wallet is constructed if the passed KeyChainGroup is empty. This means you can back up a wallet immediately after construction even before you request a key. Thanks to Andreas for the suggestion.
HDW: Add a getKeyByPath() method to wallet, and (experimental) sanity check precomputed keys before they're returned by the wallet API to guard against the potential of a bitflip in either the stored pubkey bytes, or the ECC precomputed tables. The chance of such a bit flip is small but such flips HAVE been seen in the wild against other bitcoin implementations, so it could happen to a bitcoinj user too. The consequences can be catastrophic (destroyed money) so best to try and do what we can.
Introduce Fiat as a holder for fiat values. Coin and Fiat share an interface Monetary so that monetary infrastructure can be re-used.

Adapt CoinFormat to be used with Monetary. Add an ExchangeRate value class that can convert from Coin to Fiat and back.