Remove/ignore tx version in utxo and undo

This makes the following changes:
* In undo data and the chainstate database, the transaction nVersion
  field is removed from the data structures, always written as 0, and
  ignored when reading.
* The definition of hash_serialized in gettxoutsetinfo is changed to no
  longer incude the nVersion field. It is renamed to hash_serialized_2
  to avoid confusion. The new definition also includes transaction
  height and coinbase information, as this information was missing
  before.

This depends on having a CHashVerifier-based undo data checksum
verifier.

Apart from changing the definition of serialized_hash, downgrading
after using this patch is supported, as no release ever used the value
of nVersion field in UTXO entries.

src/test/transaction_tests.cpp

@@ -471,7 +471,6 @@ BOOST_AUTO_TEST_CASE(test_big_witness_transaction) {
         threadGroup.create_thread(boost::bind(&CCheckQueue<CScriptCheck>::Thread, boost::ref(scriptcheckqueue)));
 
     CCoins coins;
-    coins.nVersion = 1;
     coins.fCoinBase = false;
     for(uint32_t i = 0; i < mtx.vin.size(); i++) {
         CTxOut txout;