PR solving the current master's syncing issue (syncing process not passing through block 5840), solved in 9d8b8a2.

Essentially, when we merged #1815, we moved from using the default transaction constructor and the ser/unser template methods (SerializationOp) to be using, inside the templated serialization puzzle, the deserializing constructor (CTransaction(deserialize_type, Stream& s)) which internally creates a CMutableTransaction which wasn't having the same sapling tx version guard as CTransaction ser/unser method. So, in other words, it was trying to parse the shielded transaction data from an old version two transaction (yes, we already have version two transaction in our network.. first one is in block 5840).

Plus, i took the mischief of not only including the bugfix, have added:

• stream::read function readability improvement coming from Refactor: simpler read bitcoin/bitcoin#11221.
• a pretty straightforward adaptation of upstream's b4e4ba4 (missing last commit not included in Make CBlock a vector of shared_ptr of CTransactions #1815).
• a PeerLogicValidation class compiler warning fix 1ca1b89