Decouple wallet version from client version

Instead of comparing version numbers in the wallet to the client
version number, compare them to the latest supported wallet version
in the client. This allows for wallet version numbers to be unrelated
to the client version number.

src/wallet/wallet.cpp

@@ -4104,7 +4104,7 @@ std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(const std::string& name,
         if (nMaxVersion == 0) // the -upgradewallet without argument case
         {
             LogPrintf("Performing wallet upgrade to %i\n", FEATURE_LATEST);
-            nMaxVersion = CLIENT_VERSION;
+            nMaxVersion = FEATURE_LATEST;
             walletInstance->SetMinVersion(FEATURE_LATEST); // permanently upgrade the wallet immediately
         }
         else

src/wallet/walletdb.cpp

@@ -537,7 +537,7 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
         int nMinVersion = 0;
         if (m_batch.Read((std::string)"minversion", nMinVersion))
         {
-            if (nMinVersion > CLIENT_VERSION)
+            if (nMinVersion > FEATURE_LATEST)
                 return DBErrors::TOO_NEW;
             pwallet->LoadMinVersion(nMinVersion);
         }
@@ -640,7 +640,7 @@ DBErrors WalletBatch::FindWalletTx(std::vector<uint256>& vTxHash, std::vector<CW
         int nMinVersion = 0;
         if (m_batch.Read((std::string)"minversion", nMinVersion))
         {
-            if (nMinVersion > CLIENT_VERSION)
+            if (nMinVersion > FEATURE_LATEST)
                 return DBErrors::TOO_NEW;
         }