Shim functions and tests added

Hi there. Love the simplicity of the Proto.js stuff. I've made a number of changes around the code you already have, but really haven't changed what you started with. Basically I added a test framework (QUnit) and moved the shim code you had for "getOwnPropertyDescriptors" (along with a bunch of other shim code) into a "shim.js" file to be included separately.

All of the current tests pass in the latest Chrome, Firefox, Opera, and IE 8 & 9 (I'll check 10 tomorrow, but I can't imagine it breaking on that version).

I have a couple of changes to the core code I'm going to make for my own benefit, but I wanted to submit the PR for this stuff first since it doesn't really change your code much (one or two lines I think).

Let me know what you think!

--Jordan