core/vm: Remove snapshot param from Interpreter.Run()

The tx data field is called "input" in returned objects and "data" in
argument objects. Make it so "input" can be used, but bail if both
are set.

accounts/keystore: Improved error message

* Fix for #15668

p2p/discover: fix leaked goroutine in data expiration

cmd/geth: add support for geth --rinkeby attach

This adds the inverse to DecompressPubkey and improves a few minor
details in crypto/secp256k1.

crypto: Fix comment typo

Fixes #15408
Fixes #14432

consensus/ethash: relax requirements when determining future-blocks

This commit adds mocker functionality to p2p/simulations. A
mocker allows to starting/stopping of nodes via the HTTP API.

This commit adds a TOML configuration option to swarm. It reuses
the TOML configuration structure used in geth with swarm
customized items.

The commit:

* Adds a "dumpconfig" command to the swarm executable which
  allows printing the (default) configuration to stdout, which
  then can be redirected to a file in order to customize it.
* Adds a "--config <file>" option to the swarm executable which will
  allow to load a configuration file in TOML format from the
  specified location in order to initialize the Swarm node The
  override priorities are like follows: environment variables
  override command line arguments override config file override
  default config.

With this change,

    key, err := crypto.HexToECDSA("000000...")
    
returns nil key and an error instead of a non-nil key with nil X
and Y inside. Issue found by @guidovranken.

Issue found by @guidovranken

Now that the AES salt has been moved to the payload, padding must
be adjusted to hide it, lest an attacker guesses that the packet
uses symmetric encryption.

As per EIP-627, the salt for symmetric encryption is now
part of the payload. This commit does that.

Also remove installation steps for fuse and golang.org/x/tools/cmd/cover 
because they're not required anymore.

Fixes #15196

We need those operations for p2p/enr.

Also upgrade github.com/btcsuite/btcd/btcec to the latest version
and improve BenchmarkSha3. The benchmark printed extra output 
that confused tools like benchstat and ignored N.

Also unexport isHex, hasHexPrefix because IsHexAddress is the only caller.

Fixes #15550

Generator in the current lib uses -2 as the y point when doing
ScalarBaseMult, this makes it so that points/signatures generated
from libs like py_ecc don't match/validate as pretty much all
other libs (including libsnark) have (1, 2) as the standard
generator.

This does not affect consensus as the generator is never used in
the VM, points are always explicitly defined and there is not
ScalarBaseMult op - it only makes it so that doing "import
github.com/ethereum/go-ethereum/crypto/bn256" doesn't generate
bad points in userland tools.

Updated use of Parallel and added some subtests to help isolate
them. Increased timeout in RequestHeadersByNumber so it
doesn't time out and causes other tests to break.