AJAX extensions to the comment module

In order to push the idea of a JavaScript preprocessor, and in order to minimize the number of actions required to do simple things, I think it would be good to extend core modules with some AJAX functions. The attached patch adds instant comment deletion. It needs some work, especially the confirmation needs to support translation, but I don't know how to do it best.

Of course this could be done with a separate module, but I still think it'd be best to have it in the core. If the idea gets accepted, I will add more functions, otherwise I'll contribute a module. If there's another similar effort, please point me to it, a brief search shows nothing related.