Create COIN_DUST constant, to represent the dust spam limit used.
Decrease COIN_DUST to 0.001 BTC
Rationale: With the increase in bitcoin value (US$13.67 as of this writing), it seems reasonable to reduce the value level of which we consider "dust spam."
- Update TX miner and relay fee defaults to 0.001 / 0.0005 BTC respectively
Rationale: Reflects growth of dust spam in unspent transaction output dataset.