requirejs patch for anonymous define()

This is the patch for my posted issue at: https://github.com/MrRio/jsPDF/issues/309

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I tried using **jsPDF** (.debug.js and .min.js) with **RequireJS** (2.1.11). Everything works fine until I use grunt to build my webapp. After minification, my webapp break with error:

![screenshot](https://cloud.githubusercontent.com/assets/1733015/3595683/1ae8b168-0cb9-11e4-9abd-2f13eff45171.png)

![screenshot-1](https://cloud.githubusercontent.com/assets/1733015/3595687/26afdd1e-0cb9-11e4-8cfa-1e4327a3fb26.png)


I found a workaround to this problem, by specifying what is called a stringID for that define() function:
```javascript
define('jsPDF', function(){
    return jsPDF;
});