Some tests take quite some time during exit, which I think causes
some appveyor fails like this:

    https://ci.appveyor.com/project/ethereum/go-ethereum/builds/39511210/job/xhom84eg2e4uulq3

One of the things that seem to take time during exit is waiting
(up to 100ms) for the syncbloom to close. This PR changes it to use
a channel, instead of looping with a 100ms wait.

This also includes some unrelated changes improving the reliability of
eth/fetcher tests, which fail a lot because they are time-dependent.

This PR removes the blockhash from the statedb

Fixes test failure in the last commit.

This commit adds the package gethclient which is similar to the ethclient
and implements some geth specific functionality.
Co-authored-by: NEdgar Aroutiounian <edgar.factorial@gmail.com>
Co-authored-by: NFelix Lange <fjl@twurst.com>

This fixes transaction sending in the case where an app using go-ethereum v1.10.4
is talking to a pre-EIP-1559 RPC node. In this case, the eth_maxPriorityFeePerGas
endpoint is not available and we can only rely on eth_gasPrice.

* eth/gasprice: implement feeHistory API

* eth/gasprice: factored out resolveBlockRange

* eth/gasprice: add sanity check for missing block

* eth/gasprice: fetch actual gas used from receipts

* miner, eth/gasprice: add PendingBlockAndReceipts

* internal/ethapi: use hexutil.Big

* eth/gasprice: return error when requesting beyond head block

* eth/gasprice: fixed tests and return errors correctly

* eth/gasprice: rename receiver name

* eth/gasprice: return directly if blockCount == 0
Co-authored-by: Nrjl493456442 <garyrong0905@gmail.com>

* core,eth/tracers: make isPrecompiled dependent on HF

* eth/tracers: use keys when constructing chain config struct

* eth/tracers: dont initialize activePrecompiles with random value

This is an obvious spelling error
Co-authored-by: Nliuyaxiong <liuyaxiong@inspur.com>

This change increases the cache size from 64 to 256 Mb for block bodies.
Benchmarks have shown this to be one bottleneck when trying to achieve
higher download speeds.

The commit also includes a minor optimization for header inserts in package
core: previously, the presence of headers in the database was checked for
every header before writing it. With the change, if one header fails the
presence check, all subsequent headers are also assumed to be missing.
This is an improvement because in practice, the headers are almost always
missing during sync.

Co-authored-by: Nlidongwei <lidongwei@huobi.com>

Previously, the test waited a second and then failed if geth had not
started. This caused the test to fail intermittently. This change checks
whether the IPC is open 10 times over a 5 second period and then fails
if geth is still not available.

* Convert int/hash values from context into js object

* Use js fixed buffer
Co-authored-by: NWilliam <william.berman@coinbase.com>

eth/tracers: expose contextual infos (block hash, tx hash, tx index)

crypto: fix build directives

accounts/abi/bind: call ensureContext on every context

The `README.md` links the Gitter channel for discussions, but the
official docs and even the Gitter channel itself recommend using the
official Discord Server for such discussions.
This PR simply changes the Gitter link and provides Discord invite link.

travis: enable experimental docker for manifest building

travis, Dockerfile, build: docker build and multi-arch publish combo

travis: move docker steps further to prevent hanging other builders

When deleting in fullNode, and the new child node nn is not nil, there is no need
to check the number of non-nil entries in the node. This is because the fullNode 
must've contained at least two children before deletion, so there must be another
child node other than nn.
Co-authored-by: NFelix Lange <fjl@twurst.com>

Copy the CliqueConfig instead of reusing the pointer.
This makes DeveloperGenesisBlock thread safe and prevents it from
changing params.AllCliqueProtocolChanges.Clique.Epoch.

travis, build: add support for multi-arch docker images