add extensions to babel-cli bin files

packages/babel-cli/src/babel-external-helpers.js

@@ -0,0 +1,11 @@
+var commander = require("commander");
+var util      = require("babel-core").util;
+var runtime   = require("babel-core").buildExternalHelpers;
+
+commander.option("-l, --whitelist [whitelist]", "Whitelist of helpers to ONLY include", util.list);
+commander.option("-t, --output-type [type]", "Type of output (global|umd|var)", "global");
+
+commander.usage("[options]");
+commander.parse(process.argv);
+
+console.log(runtime(commander.whitelist, commander.outputType));