Support loading of jasmine more than once during a page load

Hi, this prabably doesn't handle the commonJS case correctly.

But this is the change I've made to support loading jasmin.js more than once for a single page.

This fixes the issue where jasmine goes into an infinite loop on the timeout methods
https://github.com/pivotal/jasmine/issues/247

To reproduce, have a page with something like 
<script src="jasmine.js">
<script src="jasmine.js">