* 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
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).