cmd/faucet: embed git commit hash/date, disable Google+

* add-date-to unstable

* fields-insteadof-split

* internal/build: support building with missing git

* docker: add git history back to support commit date in version

* internal/build: use PR commits hashes for PR builds

* core: import known blocks if they can be inserted as canonical blocks

* core: insert knowns blocks

* core: remove useless

* core: doesn't process head block in reorg function

eth/downloader: fix header delays during chain dedup

* accounts: add note about backing up the keystore

* cmd, accounts: move the printout to accountCreate

* internal, signer: add info when new account is created via rpc

* cmd, internal, signer: split logs

* cmd/geth: make account new output a bit more verbose

* core: add tests for canonicality confusion

* core: delete stale future canon number mappings during reorg to shorter+heavier chain

* trie: fix merkle proof

* trie: use hasher instead of allocate keccack256 every time

* trie: add comments

p2p/discover: split out discv4 code

This change makes getBalance, getCode, getStorageAt, getProof,
call, getTransactionCount return an error if the block number in
the request doesn't exist. getHeaderByNumber still returns null
for missing headers.

* consensus,core,miner: avoid overhead of creating a new block

* consensus: nitpick dot

* consensus: fix some comment formatting nits

This change restructures the internals of p2p/discover to make room for
the discv5 code which will soon be added to this package.

- packet type names now have a "V4" suffix.
- ListenUDP returns *UDPv4 instead of *Table. This technically breaks
  the API but the only caller in go-ethereum is package p2p, which uses
  a compatible interface and doesn't need changes.
- The internal transport interface is changed to make Table reusable for v5.
- The 'lookup' code moves from table to transport. This required
  updating the lookup unit test to use udpTest instead of a custom transport.

eth: enforce chain above CHT before accepting txs into the pool

* typo fix

* change to stores

* swarm/network: fix data races in TestInitialPeersMsg test

* swarm/network: add Kademlia.Saturation method with lock

* swarm/network: add Hive.Peer method to safely retrieve a bzz peer

* swarm/network: remove duplicate comment

* p2p/testing: prevent goroutine leak in ProtocolTester

* swarm/network: fix data race in newBzzBaseTesterWithAddrs

* swarm/network: fix goroutone leaks in testInitialPeersMsg

* swarm/network: raise number of peer check attempts in testInitialPeersMsg

* swarm/network: use Hive.Peer in Hive.PeerInfo function

* swarm/network: reduce the scope of mutex lock in newBzzBaseTesterWithAddrs

* swarm/storage: disable TestCleanIndex with race detector

cmd/utils, node: switch over default peer count to 50

* core: lookup txs by block number instead of block hash

Transaction hashes now store a reference to their corresponding
block number as opposed to their hash. In benchmarks this was
shown to reduce storage by over 12 GB.

The main limitation of this approach is that transactions on
non-canonical blocks could never be looked up, however that is
currently not supported.

The database version has been upgraded to version 5 and the
transaction lookup process is backwards-compatible with the
prior two transaction lookup formats prexisting in the
database instance. Tests have been added to ensure this.

* core/rawdb: tiny review nit fixes

 accounts: switch Ledger derivation path to canonical one

* eth/downloader: enable unsync-protection for light client

* eth/downloader: fix tests

* cmd, eth, miner: disable advance sealing if user require

* cmd, console, miner, les, eth: wrap the miner config

* eth: remove todo

* cmd, miner: revert noadvance flag

The reason for this is: if the transaction execution is even longer
than block time, then this kind of transactions is DoS attack.

trie: approximate the wasted cache metaspace closer

eth, les, light: enforce CHT checkpoints on fast-sync too

appveyor.yml: Upgraded to Go 1.12.4