eth/downloader: exit loop when there is no more available task

internal/debug: add debug_setGCPercent

* core: only fire one chain head per batch

* miner: announce chan events synchronously

* ethdb: add Putter interface and Has method

* ethdb: improve docs and add IdealBatchSize

* ethdb: remove memory batch lock

Batches are not safe for concurrent use.

* core: use ethdb.Putter for Write* functions

This covers the easy cases.

* core/state: simplify StateSync

* trie: optimize local node check

* ethdb: add ValueSize to Batch

* core: optimize HasHeader check

This avoids one random database read get the block number. For many uses
of HasHeader, the expectation is that it's actually there. Using Has
avoids a load + decode of the value.

* core: write fast sync block data in batches

Collect writes into batches up to the ideal size instead of issuing many
small, concurrent writes.

* eth/downloader: commit larger state batches

Collect nodes into a batch up to the ideal size instead of committing
whenever a node is received.

* core: optimize HasBlock check

This avoids a random database read to get the number.

* core: use numberCache in HasHeader

numberCache has higher capacity, increasing the odds of finding the
header without a database lookup.

* core: write imported block data using a batch

Restore batch writes of state and add blocks, tx entries, receipts to
the same batch. The change also simplifies the miner.

This commit also removes posting of logs when a forked block is imported.

* core: fix DB write error handling

* ethdb: use RLock for Has

* core: fix HasBlock comment

Fixes #15004

- dao.go is already present in consensus/misc
- core/dao.go is not used anywhere in the codebase

eth: disable fast sync after pivot is committed

core/bloombits, eth/filter: transformed bloom bitmap based log search

core: use blocks and avoid deep reorgs in txpool

eth: use maxpeers from p2p layer instead of extra config

Dockerfile, cmd/puppeth: fix missing SSL certificates, use main image in puppeth

core: make txpool operate on immutable state

bmt is a new package that provides hashers for binary merkle tree hashes on
size-limited chunks. the main motivation is that using BMT hash as the chunk
hash of the swarm hash offers logsize inclusion proofs for arbitrary files on a
32-byte resolution completely viable to use in challenges on the blockchain.

Dockerfile: multi-stage builds, Go 1.9

* cmd/evm: adds ability to run individual state test file

* cmd/evm: Fix statetest runner to be more json friendly

* cmd/evm, tests: minor polishes, dump state on fail

* core/vm: Make max_codesize only applicable post Spurious Dragon/158/155/161/170

* tests: Remove expected failure

* core: Fix flaw where underpriced locals were removed

* core: minor code cleanups for tx pool tests