Closes #1957 by adding tx serialization size to listtransactions output.

src/wallet/rpcwallet.cpp

@@ -1325,6 +1325,7 @@ void ListTransactions(const CWalletTx& wtx, const string& strAccount, int nMinDe
             entry.push_back(Pair("fee", ValueFromAmount(-nFee)));
             if (fLong)
                 WalletTxToJSON(wtx, entry);
+            entry.push_back(Pair("size", static_cast<CTransaction>(wtx).GetSerializeSize(SER_NETWORK, PROTOCOL_VERSION)));
             ret.push_back(entry);
         }
     }
@@ -1361,6 +1362,7 @@ void ListTransactions(const CWalletTx& wtx, const string& strAccount, int nMinDe
                 entry.push_back(Pair("vout", r.vout));
                 if (fLong)
                     WalletTxToJSON(wtx, entry);
+                entry.push_back(Pair("size", static_cast<CTransaction>(wtx).GetSerializeSize(SER_NETWORK, PROTOCOL_VERSION)));
                 ret.push_back(entry);
             }
         }
@@ -1429,6 +1431,7 @@ Value listtransactions(const Array& params, bool fHelp)
             "    \"otheraccount\": \"accountname\",  (string) For the 'move' category of transactions, the account the funds came \n"
             "                                          from (for receiving funds, positive amounts), or went to (for sending funds,\n"
             "                                          negative amounts).\n"
+            "    \"size\": n,                (numeric) Transaction size in bytes\n"
             "  }\n"
             "]\n"