* mempool: remove only valid (Code==0) txs on Update

so evil proposers can't drop valid txs in Commit stage.

Also remove invalid (Code!=0) txs from the cache so they can be
resubmitted.

Fixes #3322

@rickyyangz:

In the end of commit stage, we will update mempool to remove all the txs
in current block.

// Update mempool.
err = blockExec.mempool.Update(
	block.Height,
	block.Txs,
	TxPreCheck(state),
	TxPostCheck(state),
)

Assum an account has 3 transactions in the mempool, the sequences are
100, 101 and 102 separately, So an evil proposal can only package the
101 and 102 transactions into its proposal block, and leave 100 still in
mempool, then the two txs will be removed from all validators' mempool
when commit. So the account lost the two valid txs.

@ebuchman:

In the longer term we may want to do something like #2639 so we can
validate txs before we commit the block. But even in this case we'd only
want to run the equivalent of CheckTx, which means the DeliverTx could
still fail even if the CheckTx passes depending on how the app handles
the ABCI Code semantics. So more work will be required around the ABCI
code. See also #2185

* add changelog entry and tests

* improve changelog message

* reformat code

* mempool: resCb -> globalCb

* reqResCb takes an externalCb

* failing test for #3509

* txsMap is sync.Map

* update changelog

Closes #1798

This is done by making every mempool tx maintain a list of peers who its received the tx from. Instead of using the 20byte peer ID, it instead uses a local map from peerID to uint16 counter, so every peer adds 2 bytes. (Word aligned to probably make it 8 bytes)

This also required resetting the callback function on every CheckTx. This likely has performance ramifications for instruction caching. The actual setting operation isn't costly with the removal of defers in this PR.

* Make the mempool not gossip txs back to peers its received it from

* Fix adversarial memleak

* Don't break interface

* Update changelog

* Forgot to add a mtx

* forgot a mutex

* Update mempool/reactor.go

Co-Authored-By: ValarDragon <ValarDragon@users.noreply.github.com>

* Update mempool/mempool.go

Co-Authored-By: ValarDragon <ValarDragon@users.noreply.github.com>

* Use unknown peer ID

Co-Authored-By: ValarDragon <ValarDragon@users.noreply.github.com>

* fix compilation

* use next wait chan logic when skipping

* Minor fixes

* Add TxInfo

* Add reverse map

* Make activeID's auto-reserve 0

* 0 -> UnknownPeerID

Co-Authored-By: ValarDragon <ValarDragon@users.noreply.github.com>

* Switch to making the normal case set a callback on the reqres object

The recheck case is still done via the global callback, and stats
are also set via global callback

* fix merge conflict

* Addres comments

* Add cache tests

* add cache tests

* minor fixes

* update metrics in reqResCb and reformat code

* goimport -w mempool/reactor.go

* mempool: update memTx senders

I had to introduce txsMap for quick mempoolTx lookups.

* change senders type from []uint16 to sync.Map

Fixes DATA RACE:

```
Read at 0x00c0013fcd3a by goroutine 183:
  github.com/tendermint/tendermint/mempool.(*MempoolReactor).broadcastTxRoutine()
      /go/src/github.com/tendermint/tendermint/mempool/reactor.go:195 +0x3c7

Previous write at 0x00c0013fcd3a by D[2019-02-27|10:10:49.058] Read PacketMsg                               switch=3 peer=35bc1e3558c182927b31987eeff3feb3d58a0fc5@127.0.0.1
:46552 conn=MConn{pipe} packet="PacketMsg{30:2B06579D0A143EB78F3D3299DE8213A51D4E11FB05ACE4D6A14F T:1}"
goroutine 190:
  github.com/tendermint/tendermint/mempool.(*Mempool).CheckTxWithInfo()
      /go/src/github.com/tendermint/tendermint/mempool/mempool.go:387 +0xdc1
  github.com/tendermint/tendermint/mempool.(*MempoolReactor).Receive()
      /go/src/github.com/tendermint/tendermint/mempool/reactor.go:134 +0xb04
  github.com/tendermint/tendermint/p2p.createMConnection.func1()
      /go/src/github.com/tendermint/tendermint/p2p/peer.go:374 +0x25b
  github.com/tendermint/tendermint/p2p/conn.(*MConnection).recvRoutine()
      /go/src/github.com/tendermint/tendermint/p2p/conn/connection.go:599 +0xcce

Goroutine 183 (running) created at:
D[2019-02-27|10:10:49.058] Send                                         switch=2 peer=1efafad5443abeea4b7a8155218e4369525d987e@127.0.0.1:46193 channel=48 conn=MConn{pipe} m
sgBytes=2B06579D0A146194480ADAE00C2836ED7125FEE65C1D9DD51049
  github.com/tendermint/tendermint/mempool.(*MempoolReactor).AddPeer()
      /go/src/github.com/tendermint/tendermint/mempool/reactor.go:105 +0x1b1
  github.com/tendermint/tendermint/p2p.(*Switch).startInitPeer()
      /go/src/github.com/tendermint/tendermint/p2p/switch.go:683 +0x13b
  github.com/tendermint/tendermint/p2p.(*Switch).addPeer()
      /go/src/github.com/tendermint/tendermint/p2p/switch.go:650 +0x585
  github.com/tendermint/tendermint/p2p.(*Switch).addPeerWithConnection()
      /go/src/github.com/tendermint/tendermint/p2p/test_util.go:145 +0x939
  github.com/tendermint/tendermint/p2p.Connect2Switches.func2()
      /go/src/github.com/tendermint/tendermint/p2p/test_util.go:109 +0x50

I[2019-02-27|10:10:49.058] Added good transaction                       validator=0 tx=43B4D1F0F03460BD262835C4AA560DB860CFBBE85BD02386D83DAC38C67B3AD7 res="&{CheckTx:gas_w
anted:1 }" height=0 total=375
Goroutine 190 (running) created at:
  github.com/tendermint/tendermint/p2p/conn.(*MConnection).OnStart()
      /go/src/github.com/tendermint/tendermint/p2p/conn/connection.go:210 +0x313
  github.com/tendermint/tendermint/libs/common.(*BaseService).Start()
      /go/src/github.com/tendermint/tendermint/libs/common/service.go:139 +0x4df
  github.com/tendermint/tendermint/p2p.(*peer).OnStart()
      /go/src/github.com/tendermint/tendermint/p2p/peer.go:179 +0x56
  github.com/tendermint/tendermint/libs/common.(*BaseService).Start()
      /go/src/github.com/tendermint/tendermint/libs/common/service.go:139 +0x4df
  github.com/tendermint/tendermint/p2p.(*peer).Start()
      <autogenerated>:1 +0x43
  github.com/tendermint/tendermint/p2p.(*Switch).startInitPeer()
```

* explain the choice of a map DS for senders

* extract ids pool/mapper to a separate struct

* fix literal copies lock value from senders: sync.Map contains sync.Mutex

* use sync.Map#LoadOrStore instead of Load

* fixes after Ismail's review

* rename resCbNormal to resCbFirstTime