If all peers have been tried during the block download process and some
hashes are unfetchable (available peers > 0 and fetching == 0) throw an
error so the process can be aborted.

* Downloader's peers keeps track of peer's previously requested hashes
  so that we don't have to re-request
* Changed `AddBlock` to be fully synchronous

* Improved block propagation by sending blocks only to peers to which, as
  far as we know, the peer does not know about.
* Made sub protocol its own manager
* SubProtocol now contains the p2p.Protocol which is used instead of
  a function-returning-protocol thing.

Conflicts:
	eth/downloader/downloader.go

add extra space to miner icon

Whisper cleanup, part 2

p2p: fix the dial timer

The dial timer was not reset properly when the peer count reached
MaxPeers.

Fix RPC Call output when empty

Update transaction tests

Properly ignore blocks coming from peers not in our peer list (blocked)
and do never request anything from bad peers. Added some checks to
account for blocks known when requesting hashes (missing parents).

Properly ignore blocks coming from peers not in our peer list (blocked)
and do never request anything from bad peers. Added some checks to
account for blocks known when requesting hashes (missing parents).