internal/ethapi: don't query wallets at every execution of gas estimation

* miner: fix data race in tests

miner: fix linter

* miner: address comment

* rpc: remove 'exported or builtin' restriction for parameters

There is no technial reason for this restriction because package reflect
can create values of any type. Requiring parameters and return values to
be exported causes a lot of noise in package exports.

* rpc: fix staticcheck warnings

Also fix the input formatter on clique_getSnapshot and clique_getSigners
so that integers as well as hex number strings are accepted.

* core/rawdb: check hash before return data from ancient db

* core/rawdb: fix lint

* core/rawdb: calculate the hash in the fly

Found by staticcheck.

Also unexport the status struct.

This PR introduces clique_status which gives info about the health of
the clique network.

It's currently a bit PITA to find out how a clique network is
performing, and it can easily happen that sealers drop off -- and
everything is 'fine' until one more signer drops off, and the network
suddenly halts.

The new method provides the following stats:

- Which signers are currently active, and have signed blocks in the last
  N (set to 64) blocks?
- How many blocks has each signer signed?
- What is the difficulty in the last N blocks, compared to the
  theoretical maximum?

Adds flags akin to -coverage flag enabling the test runner
to use go test's -v flag, signaling verbose test log output.

* core: s/isEIP155/isEIP2/ (fix)

This signature variable name reflects a spec'd change
in gas cost for creating contracts as documented in EIP2 (Homestead HF).

https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.md#specification

* core: s/isEIP2/sIsHomestead/g

Use isHomestead since Homestead is what the caller
and rest of the code uses.

* travis: remove debug traces

* travis: Add travis_wait to the test run

* travis: increase travis_wait time

* build: use golangci-lint

This changes build/ci.go to download and run golangci-lint instead
of gometalinter.

* core/state: fix unnecessary conversion

* p2p/simulations: fix lock copying (found by go vet)

* signer/core: fix unnecessary conversions

* crypto/ecies: remove unused function cmpPublic

* core/rawdb: remove unused function print

* core/state: remove unused function xTestFuzzCutter

* core/vm: disable TestWriteExpectedValues in a different way

* core/forkid: remove unused function checksum

* les: remove unused type proofsData

* cmd/utils: remove unused functions prefixedNames, prefixFor

* crypto/bn256: run goimports

* p2p/nat: fix goimports lint issue

* cmd/clef: avoid using unkeyed struct fields

* les: cancel context in testRequest

* rlp: delete unreachable code

* core: gofmt

* internal/build: simplify DownloadFile for Go 1.11 compatibility

* build: remove go test --short flag

* .travis.yml: disable build cache

* whisper/whisperv6: fix ineffectual assignment in TestWhisperIdentityManagement

* .golangci.yml: enable goconst and ineffassign linters

* build: print message when there are no lint issues

* internal/build: refactor download a bit

* rpc: improve codec abstraction

rpc.ServerCodec is an opaque interface. There was only one way to get a
codec using existing APIs: rpc.NewJSONCodec. This change exports
newCodec (as NewFuncCodec) and NewJSONCodec (as NewCodec). It also makes
all codec methods non-public to avoid showing internals in godoc.

While here, remove codec options in tests because they are not
supported anymore.

* p2p/simulations: use github.com/gorilla/websocket

This package was the last remaining user of golang.org/x/net/websocket.
Migrating to the new library wasn't straightforward because it is no
longer possible to treat WebSocket connections as a net.Conn.

* vendor: delete golang.org/x/net/websocket

* rpc: fix godoc comments and run gofmt

Make it possible to load input from a file. Simlar to `--code` / `--codefile`, have `--input`/`--inputfile`.