This resolves a major source of pain with Blockstream, though it does mean that it depends on very new versions of Geth/Parity that have this functionality.

…` rather than throwing an error.

`parseInt` is terrible and refuses to ever throw if something goes wrong, instead preferring to return "something reasonable" (which often times is completely unreasonable).  This change doesn't solve all of parseInt's problems, but it at least stops it from returning `NaN` or `Infinity`.