prevent users from misconfiguring their nodes so that fork ordering is not preserved.

In Geth, we have two sources for configuration:
(1) Config file
(2) Command line flag

Basically geth will first resolve config file and then overwrite
configs with command line flags.

This issue is: geth should only overwrite configs if flags are truly
set. So before we apply any flag to configs, `GlobalIsSet` check
is necessary.

* update tests for istanbul

* tests: updated blockchaintests, see https://github.com/ethereum/tests/issues/637

* tests: update again, hopefully fixed this time

* tests: skip time consuming, run legacy tests

* tests: update again

* build: disable long-running tests on travis

* tests: fix formatting nits

* tests: I hate github's editor

p2p: measure subprotocol bandwidth usage

* vendor: update leveldb

* ethdb/leveldb: disable seek compaction and add metrics

* vendor: udpate latest levledb

* ethdb/leveldb: fix typo

This change adds support for EIP-1898. 

Fixes #18210

This adds an implementation of node discovery via DNS TXT records to the
go-ethereum library. The implementation doesn't match EIP-1459 exactly,
the main difference being that this implementation uses separate merkle
trees for tree links and ENRs. The EIP will be updated to match p2p/dnsdisc.

To maintain DNS trees, cmd/devp2p provides a frontend for the p2p/dnsdisc
library. The new 'dns' subcommands can be used to create, sign and deploy DNS
discovery trees.

dashboard: log dashboard url

* core/state: revert noop finalise, fix copy-commit-copy

* core/state: reintroduce net sstore tracking, extend tests for it

params: remove legacy bootnodes

deepCopy didn't copy pending storage updates, leading to the
creation of blocks with invalid state root.

vendor: pull in USB Windows fixes

params: activate Istanbul on Ropsten, Rinkeby and Görli

params: bump CHTs for the 1.9.4 release

core: fix tx dedup return error count

* les: detailed relative cost metrics

* les: filter txpool relative request statistic

* les: initialize price factors

* les: increased connected bias to lower churn rate

* les: fixed clientPool.setLimits

* core: do not use mutex in GetAncestor

* les: bump factor db version again

* les: add metrics

* les, light: minor fixes

core: dedup known transactions without global lock, track metrics