DRY-up the use of fromHex in the project

Was previously returning nonsensical “0x”

This depends on a change in ethash which exposes UpdateCache.

This allows changing the config before starting Ethereum
with it.

There is no reason to keep them as ethutil.Bytes.

NatSpec integration

* Reimplemented nonce management for known accounts.

* Cleaned up VM execution. VM run now takes a context
* ADDMOD/MULMOD - removed incorrect cast

Allow returning different JSON RPC error codes depending on error type

0749546 random fails
a153865 random fails

git-subtree-dir: tests/files
git-subtree-split: 074954630f43e97f0769997d175511a00a47cc9d