Add UMD Support for CommonJS

Ok, I think I see what is your intention was. To my understanding, if you are using AMD in the browser and the call to jQuery fails, it will only result in a 404, however if you are running a build script (r.js or almond) on it, the and the call to jQuery fails, the entire build will fail. By this logic, the code as you have it will not work for developers who are using an AMD build script that doesn't have doesn't have jQuery as a dependency.