Fix chains where the difficulty has risen above the 100 bitlength (#44)

eth/protocols/eth/handshake.go

@@ -69,7 +69,7 @@ func (p *Peer) Handshake(network uint64, td *big.Int, head common.Hash, genesis
 
 	// TD at mainnet block #7753254 is 76 bits. If it becomes 100 million times
 	// larger, it will still fit within 100 bits
-	if tdlen := p.td.BitLen(); tdlen > 100 {
+	if tdlen := p.td.BitLen(); tdlen > 200 {
 		return fmt.Errorf("too large total difficulty: bitlen %d", tdlen)
 	}
 	return nil