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

- add peer switch channel arg to activateChain - no peer locking within
- proper locking in AddBlock - fixes deadlock issue
- comment out TD check and skip incorrect TD test again for hotfix

- queued       bool // flag for blockpool to skip TD check
- set to true when future block queued
- in checkTD: skip check if queued
- TODO: add test (insertchain sets future block)

- TestPeerPromotionByTdOnBlock renamed and skipped for now test should pass iff
  if TD is updated based on an agreement
- senders register in AddBlock, flag records if they are coming from newblock
  message (and therefore advertise their TD with the block) or block message
  (TODO: latter are stored on the cache and updated by checkTD call;
  protocol should also call AddBlock on newblock messages by non-best peers)
- remove TD update from optional TD field in addBlock: this is no longer part of
  the eth protocol spec -> TODO: reflect in wiki
- only initialise peer map if at least two

- do not break from headsection on error
[remove peer after protocol quit will close switchC, until then head block can arrive and block on channel while keeping peers lock causing a deadlock.]
- more careful locking in AddBlock

Support for import/export hex encoded keys

Add path expansion support for command line arguments, closes 567

Removed the from as a requiremet from the RPC eth_call. Xeth#Call now
also default values to:

1. Supplied account
2. First account if any
3. No managed account => 000000..00

The transaction pool will now some easily be able to pre determine the
validity of a transaction by checking the following:

* Account existst
* gas limit higher than the instrinsic gas
* enough funds to pay upfront costs
* nonce check

Logs are now recorded per transactions instead of tossing them out after
each transaction. This should also fix an issue with
`eth_getFilterLogs` (#629) Also now implemented are the `transactionHash,
blockHash, transactionIndex, logIndex` on logs. Closes #654.

* GetNonce Returns the canonical nonce
* SetNonce Set the managed account's nonce

Add IsOnCurve check to EC unmarshalling in ECIES decryption

Transaction pool will attempt to ignore invalid transactions it had
previously encountered.

Forward and log EC recover err and remove dup pubkey len check

libsecp256k1 #define NDEBUG