Fix binary string comparison failure

While replacing replacing [bitpay/bitcore](https://github.com/bitpay/bitcore/)'s base58 lib with ```base58-native``` as a dep, their tests failed due to this patch:
https://github.com/bitpay/bitcore/issues/402

It seems that comparing strings generated with ```Buffer.toString()``` will give false positives for some special characters. Their solution was to encode the bytes as hex before comparison.

```js
new Buffer('94', 'hex').toString() == new Buffer('93', 'hex').toString()
true

new Buffer('94', 'hex').toString('hex') == new Buffer('93', 'hex').toString('hex')
false
```