Blocktests are now integrated in cmd/ethereum.

The generic pointer decoder did not advance the input position
for empty values. This can lead to strange issues and even
infinite loops.

Merge branch 'frontier/blockpool' of https://github.com/ethersphere/go-ethereum into ethersphere-frontier/blockpool

Conflicts:
	rpc/api.go

I don't see why we would need two different accessors for a public field.

This makes Value 24 bytes smaller on 64bit systems.

Value.{Encode,Decode} are gone. It implements rlp.Encoder and rlp.Decoder
instead, so Value can be decoded into directly.

This seems to be the last remaining use of it.

- add ErrIncorrectTD
- checkTD called after insertChain successful
- fix tests, use blockPoolTester.tds to map block index to TD

- update blockpool td by subscribing to ChainHeadEvent
- if ahead of best peer, demote it
- addPeer now take own td as current td
- removePeer now take own td as current td
- add relevant tests to peers_test
- eth: backend now calls blockpool with eth.eventMux and chainManager.Td

 peer suspension to disallow reconnect after disconnect on fatal error for set period (PeerSuspensionInterval)