Use negative fees with listtransaction result types.
Use negative fees with listtransaction result types.

This matches Bitcoin Core Wallet.

Fixes #272.

btcsuite/btcwallet,jrick/btcwallet,synrg-labs/btcwallet,Roasbeef/btcwallet,decred/dcrwallet,btcsuite/btcwallet,Stash-Crypto/btcwallet,decred/dcrwallet,jrick/dcrwallet,synrg-labs/btcwallet,Stash-Crypto/btcwallet,jrick/btcwallet,jrick/dcrwallet,Roasbeef/btcwallet