Include babelify step in browserify calls

This allows using ES6 syntax in our code, while maintaining backwards
compatibility for the generated file.

check-node-version.js

@@ -0,0 +1,16 @@
+"use strict";
+
+var v = process.version;
+v = v.replace(/^v/,"");
+v = v.split(".");
+v = v.map(function(s){
+    return parseInt(s);
+});
+var a = v[0], b = v[1], c = v[2];
+if (a < 6 || (a == 6 && b < 5)) {
+    console.error("Node 6.5 or later required for development. " +
+                  "Version " + process.version + " found");
+    process.exit(1);
+} else {
+    console.log("OK");
+}