* Miners could stall because the worker wasn't aware the miner was done

c6d9629 added another test

git-subtree-dir: tests/files
git-subtree-split: c6d96293710a37489fa3b074a9fc228e0393f152

rlp: encode nil array pointers as empty list or string

XEth cleanup

bugfix with idle too long triggered after peer switch

* In case of uncle mining (e.g. same TS) the miner would stop if all
  threads happened to mine a potential uncle

- reset bestIdleTimer when launching head section process
- log chain head events
- common.Hash key in activateChain map

Update ethash lib