/// Check whether the session should bother grabbing blocks.
boolshouldGrabBlocks()const;
/// Check whether the session should bother grabbing blocks from a peer.
boolshouldGrabBlocks(EthereumPeer*_peer)const;
/// Attempt to begin syncing with the peer; first check the peer has a more difficlult chain to download, then start asking for hashes, then move to blocks