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

Add app_options to GenesisDoc

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

rpc/client: use compile time assertions instead of methods

Fixes https://github.com/tendermint/tendermint/issues/747
Updates https://github.com/tendermint/tendermint/issues/693

* Document the unmentioned limits for ConsensusParams.Validate()
* Make the limit for ConsensusParams.BlockSizeParams.MaxBytes
clear at 100MiB

https://github.com/tendermint/tendermint/pull/676#discussion_r144411458

also remove the comment

```
jaekwon
Yeah we should definitely expose ChainID.
ConsensusParams is small enough, we can just write it.
```
https://github.com/tendermint/tendermint/pull/676#discussion_r144123203

- remove state#GenesisDoc() method

Fixes #671

Unexpose GenesisDoc and ChainID fields to avoid them being
serialized to the DB on every block write/state.Save()

A GenesisDoc can now be alternatively written to the state's
database, by serializing its JSON as a value of key "genesis-doc".

There are now accessors and a setter for these attributes:
- state.GenesisDoc() (*types.GenesisDoc, error)
- state.ChainID() (string, error)
- state.SetGenesisDoc(*types.GenesisDoc)

This is a breaking change since it changes how the state's
serialization and requires that if loading the GenesisDoc entirely
from the database, you'll need to set its value in the database
as the GenesisDoc's JSON marshaled bytes.

types/heartbeat: test all Heartbeat functions

support historical abci queries