TxBuilder: add setVersion

src/transaction_builder.js

@@ -163,6 +163,13 @@ TransactionBuilder.prototype.setLockTime = function (locktime) {
   this.tx.locktime = locktime
 }
 
+TransactionBuilder.prototype.setVersion = function (version) {
+  typeforce(types.UInt32, version)
+
+  // XXX: this might eventually become more complex depending on what the versions represent
+  this.tx.version = version
+}
+
 TransactionBuilder.fromTransaction = function (transaction, network) {
   var txb = new TransactionBuilder(network)