This a fix for an attack vector where the discovery protocol could be
used to amplify traffic in a DDOS attack. A malicious actor would send a
findnode request with the IP address and UDP port of the target as the
source address. The recipient of the findnode packet would then send a
neighbors packet (which is 16x the size of findnode) to the victim.

Our solution is to require a 'bond' with the sender of findnode. If no
bond exists, the findnode packet is not processed. A bond between nodes
α and β is created when α replies to a ping from β.

This (initial) version of the bonding implementation might still be
vulnerable against replay attacks during the expiration time window.
We will add stricter source address validation later.

The primary motivation for doing this right now is that old PoC 8
nodes and newer PoC 9 nodes keep discovering each other, causing
handshake failures.

Issue #613

Frontier/sec 29

- add validation on TxMsg checking for nil
- add test for nil transaction
- add test for zero value transaction (no extra validation needed)

- rename Validate -> ValidateFields not to confure consensus block validation
- add nil transaction and nil uncle header validation
- remove bigint field checks: rlp already decodes *big.Int to big.NewInt(0)
- add test for nil header, nil transaction

- add validate method to types.Block
- validate after Decode -> error
- add tests for NewBlockMsg

Frontier/513

Configurable CORS domain

Actually verifies output as by regex

* Added new CreateAccount method which properly overwrites previous
  accounts (excluding balance)
* Fixed block tests (100% success)

Improving this in the future will allow for cleaning up a bit of legacy
code.

Now formats based on underlying hexdata or hexnum type. Fields directly
with respective constructors that cover from native types

Benefits from automatic output formatting differences between
quantities and data

29da5ea add JS block test example as state test
04108e0 Merge remote-tracking branch 'origin' into develop
6da7f35 JS failures
22b5dfc stQuadraticComplexity Refill with latest develop
c97bf26 Memory / Solidity Test Update

git-subtree-dir: tests/files
git-subtree-split: 29da5ea53ab36d74bd3c0712337168086cabfb8d