Implementation spec of Double Signing Risk Reduction [ADR-51](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-051-double-signing-risk-reduction.md) by B-Harvest
- Add `DoubleSignCheckHeight` config variable to ConsensusConfig for "How many blocks looks back to check existence of the node's consensus votes when before joining consensus"
- Add `consensus.double_sign_check_height` to `config.toml` and `tendermint node` as flag for set `DoubleSignCheckHeight`
- Set default `consensus.double_sign_check_height` to `0`  ( it could be adjustable in this PR, disable when 0  )

Refs

- [ADR-51](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-051-double-signing-risk-reduction.md)
- [https://github.com/tendermint/tendermint/issues/4059](https://github.com/tendermint/tendermint/issues/4059)
- [https://github.com/tendermint/tendermint/pull/4262](https://github.com/tendermint/tendermint/pull/4262)

* validate reactor messages

Refs #2683

* validate blockchain messages

Refs #2683

* validate evidence messages

Refs #2683

* todo

* check ProposalPOL and signature sizes

* add a changelog entry

* check addr is valid when we add it to the addrbook

* validate incoming netAddr (not just nil check!)

* fixes after Bucky's review

* check timestamps

* beef up block#ValidateBasic

* move some checks into bcBlockResponseMessage

* update Gopkg.lock

Fix

```
grouped write of manifest, lock and vendor: failed to export github.com/tendermint/go-amino: fatal: failed to unpack tree object 6dcc6ddc14
```

by running `dep ensure -update`

* bump year since now we check it

* generate test/p2p/data on the fly using tendermint testnet

* allow sync chains older than 1 year

* use full path when creating a testnet

* move testnet gen to test/docker/Dockerfile

* relax LastCommitRound check

Refs #2737

* fix conflicts after merge

* add small comment

* some ValidateBasic updates

* fixes

* AppHash length is not fixed

This reverts commit d02c5d1e30.

This reverts commit 96a3502

* Switch ports 466xx to be 266xx
This is done so the default ports aren't in the linux kernel's default ephemeral port range.

* Update ABCI import

* Bump cache on circleci

* Get more verbose output for debugging

* Bump abci dependency

* Fix accidental change of a block header's hash

* pin abci release

* Reformated the ResultStatus

* fix misuse of ResultStatus.

* updated changelog

* Fixed tests

* fixed rpc helper tests

* fixed rpc_tests

* fixed mock/status_test

* fixed typo

* fixed ommitempty on validatorstatus and the changelog

* fixed extra line in changelog

* Updated usage of the /status json response in tests after breaking changes

* Updated remaining tests with changes after searching the codebase for usage

* Reformated the ResultStatus

* fix misuse of ResultStatus.

* updated changelog

* Fixed tests

* fixed rpc helper tests

* fixed rpc_tests

* fixed mock/status_test

* fixed typo

* fixed ommitempty on validatorstatus and the changelog

* Updated usage of the /status json response in tests after breaking changes

* Updated remaining tests with changes after searching the codebase for usage

* rebased against develop

* de-mystify tests & run them in parallel (#1031)

* test optimization for jenkins (#1093)

* makefile cleanup

* tests: split fast and slow go tests, closes #1055

* pr comments

* restore circle conditions

* fix need_abci

* ...

* docker run: no :Z for circle?

* Remove cmd breaking comment

* remove accidental binary

* docs: s/Dummy&dummy/KVStore&kvstore/g

* glide update to abci

* update abci import paths

* dummy begone, hello kvstore

* RequestInitChain needs genesisBytes

* glide update

* expose AuthEnc in the P2P config

if AuthEnc is true, dialed peers must have a node ID in the address and
it must match the persistent pubkey from the secret handshake.

Refs #1157

* fixes after my own review

* fix docs

* fix build failure

```
p2p/pex/pex_reactor_test.go:288:88: cannot use seed.NodeInfo().NetAddress() (type *p2p.NetAddress) as type string in array or slice literal
```

* p2p: introduce peerConn to simplify peer creation

* Introduce `peerConn` containing the known fields of `peer`
* `peer` only created in `sw.addPeer` once handshake is complete and NodeInfo is checked
* Eliminates some mutable variables and makes the code flow better
* Simplifies the `newXxxPeer` funcs
* Use ID instead of PubKey where possible.
        * SetPubKeyFilter -> SetIDFilter
        * nodeInfo.Validate takes ID
        * remove peer.PubKey()

* persistent node ids

* fixes from review

* test: use ip_plus_id.sh more

* fix invalid memory panic during fast_sync test

```
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: panic: runtime error: invalid memory address or nil pointer dereference
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x98dd3e]
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]:
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: goroutine 3432 [running]:
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.newOutboundPeerConn(0xc423fd1380, 0xc420933e00, 0x1, 0x1239a60, 0
xc420128c40, 0x2, 0x42caf6, 0xc42001f300, 0xc422831d98, 0xc4227951c0, ...)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/peer.go:123 +0x31e
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.(*Switch).addOutboundPeerWithConfig(0xc4200ad040, 0xc423fd1380, 0
xc420933e00, 0xc423f48801, 0x28, 0x2)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:455 +0x12b
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.(*Switch).DialPeerWithAddress(0xc4200ad040, 0xc423fd1380, 0x1, 0x
0, 0x0)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:371 +0xdc
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.(*Switch).reconnectToPeer(0xc4200ad040, 0x123e000, 0xc42007bb00)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:290 +0x25f
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: created by github.com/tendermint/tendermint/p2p.(*Switch).StopPeerForError
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:256 +0x1b7
```

- we only use seeds if we can’t connect to peers in the addrbook.
- we always connect to nodes given in config/flags

Refs #864