Modified tests

I have modified the tests in order to reflect latest changes in src:

* Added a test to verify that ``navigator.getUserMedia`` is a ``function`` when supported by the browser and that it is ``undefined`` when not supported by the browser.
* Modified "Really works" test in order to make it work correclty in Firefox and Firefox Nightly (kind of dirty, though).
* Removed "first param is object" test since Opera now supports both string and object as a parameter (and document it with object param).

Tests are working/passing as expected in Phantom, Firefox, Opera, Chrome and Safari.

Thanks for #5, by the way.