Prior to this change, eth_call changed the balance of the sender account in the
EVM environment to 2^256 wei to cover the gas cost of the call execution.
We've had this behavior for a long time even though it's super confusing.

This commit sets the default call gasprice to zero instead of updating the balance,
which is better because it makes eth_call semantics less surprising. Removing
the built-in balance assignment also makes balance overrides work as expected.

Signed-off-by: meows <b5c6@protonmail.com>

Dynamic state snapshots

* core/state/snapshot/iterator: fix two disk iterator flaws

* core/rawdb: change SnapshotStoragePrefix to avoid prefix collision with preimagePrefix

This just prevents a false negative ERROR warning when, for some unknown
reason, a user attempts to turn on the module rpc even though it's already going
to be on.

These tests occasionally fail on Travis.

internal/web3ext: fix clique console apis to work on missing arguments

core/rawdb: fix freezer table test error check

eth: when triggering a sync, check the head header TD, not block

This PR fixes issues in TableDatabase.

TableDatabase is a wrapper of underlying ethdb.Database with an additional prefix.
The prefix is applied to all entries it maintains. However when we try to retrieve entries
from it we don't handle the key properly. In theory the prefix should be truncated and
only user key is returned. But we don't do it in some cases, e.g. the iterator and batch
replayer created from it. So this PR is the fix to these issues.

Fixes: Condition is always 'false' because 'err' is always 'nil'

This revision of go-duktype fixes the following warning

```
duk_logging.c: In function ‘duk__logger_prototype_log_shared’:
duk_logging.c:184:64: warning: ‘Z’ directive writing 1 byte into a region of size between 0 and 9 [-Wformat-overflow=]
  184 |  sprintf((char *) date_buf, "%04d-%02d-%02dT%02d:%02d:%02d.%03dZ",
      |                                                                ^
In file included from /usr/include/stdio.h:867,
                 from duk_logging.c:5:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:36:10: note: ‘__builtin___sprintf_chk’ output between 25 and 85 bytes into a destination of size 32
   36 |   return __builtin___sprintf_chk (__s, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   37 |       __bos (__s), __fmt, __va_arg_pack ());
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

go.mod: update golang.org/x/crypto to fix a Go 1.14 race rejection

eth: fix transaction announce/broadcast goroutine leak

This is supposed to fix the occasional failures in 
TestCancel* on Travis CI.

Includes difficulty tests for EIP2384 aka MuirGlacier.

typo in func name in the comment