Dupeout txs should be treated differently in the mempool.

1. they should be gossiped widely and repeatedly and not subject to the ordered multicast of other txs
2. they should be prioritized so proposers include them and put them first
3. we should have additional rules for adapting validator strategies to ensure dupeouts get in and get in early. Perhaps we want to force them to be at the beginning of the block so we have no weird state changes later in the bloc; perhaps we want people to start voting nil once they see a dupeout until it gets included, etc.
4. if we see dupeouts for +1/3 validators we start a RebootReactor on the switch to gossip polka proofs and establish a new genesis.json with +1/2 validators.