! transactions fixes

modules/database.js

@@ -9,9 +9,15 @@ db.loadDatabase(function (err) {
   // Now commands will be executed
 });
 
+// index the block field
 db.ensureIndex({ fieldName: 'block' }, function (err) {
   // If there was an error, err is not null
 });
+
+// index the txhash field
+db.ensureIndex({ fieldName: 'txhash', unique: true }, function (err) {
+  // If there was an error, err is not null
+});
   
 ipcMain.on('storeTransaction', (event, arg) => {
   db.update({ txhash: arg.txhash }, arg, { upsert: true }, function (err, numReplaced, upsert) {