Missing public-key type in sending ValidatorUpdate Tx

[torao]

Related to fix #101, there is a code where the ValidatorUpdate transaction in which public key type is dropped is put into the mempool and it's restored as hard-coded ed25519 on the receiver side. For instance, the tx is encoded by MakeValSetChangeTx(),

func MakeValSetChangeTx(pubkey types.PubKey, power int64) []byte {
  pubStr := base64.StdEncoding.EncodeToString(pubkey.Data)
  return []byte(fmt.Sprintf("val:%s!%d", pubStr, power))
}

it'll be distributed via mempool, and restored by Ed25519ValidatorUpdate().

func Ed25519ValidatorUpdate(pubkey []byte, power int64) ValidatorUpdate {
  return ValidatorUpdate{
    PubKey: PubKey{
      Type: "ed25519",
      Data: pubkey,
    },
    Power: power,
  }
}

This issue is different from the nature of #101, so in #101 I simply changed ed25519 to composite. But we should be able to hand over the keys correctly.

• If this operation is only performed on a test or staging environment, then we should pass and restore the public key type correctly (if possible, in a way where it's already implemented like ProtocolBuffers). And we'd like to be sure that it'll be encoded in a different way in the production environment.
• If this operation is performed on the production environment, then we'd like to know whether there are side-effects for ABCI protocol and the Cosmos-SDK by fixing addition the key-type into the tx.

[egonspace]

ValidatorUpdate tx is processed in cosmos-sdk(x/staking module).
These two functions are only for test or persistent_kvstore(sample app in tendermint).
Of course, these codes should be changed if public key is changed to the composite key.
I think it should be handled together in PR that changes to a composite key.