fix panic: failed to determine gopath: exec: "go"

```
-bash-4.2$ tendermint show_validators
panic: failed to determine gopath: exec: "go": executable file not found in $PATH

goroutine 1 [running]:
github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common.gopath(0xc4200632c0, 0x18)
	/var/lib/jenkins/workspace/03.Build.Package/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common/os.go:26 +0x1b5
github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common.init()
	/var/lib/jenkins/workspace/03.Build.Package/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common/os.go:17 +0x13c
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.init()
	/var/lib/jenkins/workspace/03.Build.Package/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/wire.go:165 +0x50
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/data.init()
	/var/lib/jenkins/workspace/03.Build.Package/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/data/wrapper.go:89 +0x50
github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/cli.init()
	/var/lib/jenkins/workspace/03.Build.Package/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/cli/setup.go:190 +0x76
main.init()
	/var/lib/jenkins/workspace/03.Build.Package/go/src/github.com/tendermint/tendermint/cmd/tendermint/main.go:42 +0x49```

An error message instead would be nice.
```

Now GoPath() is a function instead of a variable.

Change log level to Info when proposal block hashing fails

blockchain reactor timeout

Fixes https://github.com/tendermint/tendermint/issues/751.

Adds jitter to our exponential backoff to mitigate a self DDOS
vector. The jitter is a randomly picked percentage of a second
whose purpose is to ensure that each exponential backoff retry
occurs within (1<<attempts) == 2**attempts, but with the delay
each client will have a random buffer time before it tries to
reconnect instead of all at once reconnections that might even
bring back the previous conditions that might have caused the
dial to the WSServer to have failed e.g
* Network outage
* File descriptor exhaustion
* False positives from firewalls
etc

moar docs updates

docs: update abci example details

Add app_options to GenesisDoc

change echo format in build.sh script

updated test_data/build.sh script

types: ConsensusParams test + document the ranges/limits

Cleanup of code and code docs

Feature/merkleeyes to iavl

This cleans up some of the code in the state package

WIP: only notify when there are some txs (Refs #753)

Make RPCError an actual error and don't swallow its companion data

https://github.com/tendermint/tendermint/issues/762#issuecomment-338276055
```
E[10-19|04:52:38.969] Stopping peer for error                      module=p2p peer="Peer{MConn{178.62.46.14:46656} B14916FAF38A out}" err="Error: runtime error: invalid memory address or nil pointer dereference\nStack: goroutine 529485 [running]:\nruntime/debug.Stack(0xc4355cfb38, 0xb463e0, 0x11b1c30)\n\t/usr/local/go/src/runtime/debug/stack.go:24 +0xa7\ngithub.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p.(*MConnection)._recover(0xc439a28870)\n\t/home/ubuntu/go/src/github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p/connection.go:206 +0x6e\npanic(0xb463e0, 0x11b1c30)\n\t/usr/local/go/src/runtime/panic.go:491 +0x283\ngithub.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/blockchain.(*bpPeer).decrPending(0x0, 0x381)\n\t/home/ubuntu/go/src/github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/blockchain/pool.go:376 +0x22\ngithub.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/blockchain.(*BlockPool).AddBlock(0xc4200e4000, 0xc4266d1f00, 0x40, 0xc432ac9640, 0x381)\n\t/home/ubuntu/go/src/github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/blockchain/pool.go:215 +0x139\ngithub.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/blockchain.(*BlockchainReactor).Receive(0xc42050a780, 0xc420257740, 0x1171be0, 0xc42ff302d0, 0xc4384b2000, 0x381, 0x1000)\n\t/home/ubuntu/go/src/github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/blockchain/reactor.go:160 +0x712\ngithub.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p.createMConnection.func1(0x11e5040, 0xc4384b2000, 0x381, 0x1000)\n\t/home/ubuntu/go/src/github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p/peer.go:334 +0xbd\ngithub.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p.(*MConnection).recvRoutine(0xc439a28870)\n\t/home/ubuntu/go/src/github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p/connection.go:475 +0x4a3\ncreated by github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p.(*MConnection).OnStart\n\t/home/ubuntu/go/src/github.com/cosmos/gaia/vendor/github.com/tendermint/tendermint/p2p/connection.go:170 +0x187\n"
```

all, state: unexpose GenesisDoc, ChainID fields make them accessor methods

add tm-migrator to docs

correct an error in validator's specification [ci skip] (Refs #756)