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/rest.cpp

@@ -42,7 +42,6 @@ static const struct {
 };
 
 struct CCoin {
-    uint32_t nTxVer; // Don't call this nVersion, that name has a special meaning inside IMPLEMENT_SERIALIZE
     uint32_t nHeight;
     CTxOut out;
 
@@ -51,7 +50,8 @@ struct CCoin {
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action)
     {
-        READWRITE(nTxVer);
+        uint32_t nTxVerDummy = 0;
+        READWRITE(nTxVerDummy);
         READWRITE(nHeight);
         READWRITE(out);
     }
@@ -519,7 +519,6 @@ static bool rest_getutxos(HTTPRequest* req, const std::string& strURIPart)
                     // Safe to index into vout here because IsAvailable checked if it's off the end of the array, or if
                     // n is valid but points to an already spent output (IsNull).
                     CCoin coin;
-                    coin.nTxVer = coins.nVersion;
                     coin.nHeight = coins.nHeight;
                     coin.out = coins.vout.at(vOutPoints[i].n);
                     assert(!coin.out.IsNull());
@@ -568,7 +567,6 @@ static bool rest_getutxos(HTTPRequest* req, const std::string& strURIPart)
         UniValue utxos(UniValue::VARR);
         BOOST_FOREACH (const CCoin& coin, outs) {
             UniValue utxo(UniValue::VOBJ);
-            utxo.push_back(Pair("txvers", (int32_t)coin.nTxVer));
             utxo.push_back(Pair("height", (int32_t)coin.nHeight));
             utxo.push_back(Pair("value", ValueFromAmount(coin.out.nValue)));