The BreadWallet-based DigiByte Android/iOS apps used HMAC-SHA512 key
"DigiByte seed" (not BIP32's "Bitcoin seed") when turning the BIP39 seed
into the master node, so the same 12 words give a different key tree and
a standard m/0' scan finds nothing. rootFromSeed() takes an optional HMAC
key; balance scan, history, send and the derivation-path search now
cover m/0' under both keys, and user-added extra paths carry the key.