Add synced key to getinfo+getblockchaininfo

This addresses #3 of upstream issue
https://github.com/zcash/zcash/issues/3996 .

Any software that creates a transaction outside of the RPC interface
MUST check if synced==true beforehand, otherwise metadata leakage which
leads to linkability analysis is possible.

The z_sendmany, z_shieldcoinbase and z_mergetoaddress RPCs have their
own synced checks, so it's not needed to look at this new synced value
when using those RPCs.

src/rpc/blockchain.cpp

@@ -48,6 +48,7 @@
 
 using namespace std;
 
+extern int32_t KOMODO_INSYNC;
 extern void TxToJSON(const CTransaction& tx, const uint256 hashBlock, UniValue& entry);
 void ScriptPubKeyToJSON(const CScript& scriptPubKey, UniValue& out, bool fIncludeHex);
 #include "komodo_defs.h"
@@ -1689,6 +1690,7 @@ UniValue getblockchaininfo(const UniValue& params, bool fHelp)
     UniValue obj(UniValue::VOBJ);
     obj.push_back(Pair("chain",                 Params().NetworkIDString()));
     obj.push_back(Pair("blocks",                (int)chainActive.Height()));
+    obj.push_back(Pair("synced",                KOMODO_INSYNC!=0));
     obj.push_back(Pair("headers",               pindexBestHeader ? pindexBestHeader->GetHeight() : -1));
     obj.push_back(Pair("bestblockhash",         chainActive.LastTip()->GetBlockHash().GetHex()));
     obj.push_back(Pair("difficulty",            (double)GetNetworkDifficulty()));
@@ -2082,4 +2084,4 @@ void RegisterBlockchainRPCCommands(CRPCTable &tableRPC)
 {
     for (unsigned int vcidx = 0; vcidx < ARRAYLEN(commands); vcidx++)
         tableRPC.appendCommand(commands[vcidx].name, &commands[vcidx]);
-}
+}