Some testnet blocks larger than MAX_SIZE

[srya-b]

Testnet blocks such as blocks 1060697, 1060695, and 1060694 can't be deserialized because their size exceeds MAX_SIZE.

bitcoin.core.serialize.SerializationError: Asked to read 0x19abb703ff bytes; MAX_SIZE exceeded

This error occurs through rpc when trying proxy.getblock(proxy.getbestblockhash()).

[srya-b]

This also appears to be an issue arising from segwit. After using PR #112 block this problem disappears.