core: transaction pool fixes & resending transactions

Ethash reloaded

jsre: support for setTimeout, sendAsync 

added and eval queue for serializing JSRE vm execution

cmd/geth: colorize console output in windows

eth, eth/downloader: error handlers and td checks

If a peer fails to respond (disconnect, etc) during hash downloading
switch to a different peer which has it's current_hash in the queue's
peer set.

The downloader is no longer responsible for processing blocks. The
eth-protocol handler now takes care of this instead.

Added graceful shutdown during block processing. Closes #846

Peers in the eth protocol handler are now being ignored for catch up.

eth/downloader: missing parent improvement

p2p.Msg.ReceivedAt can be used for determining block propagation from
begining to end.