Added test user garbage collection to test suite

Cleaned up the test suite a bit and added garbage collection of the test user so that our apps don't get maxed out with phpunit test users as was happening in my app.

![Too many test users](https://cloud.githubusercontent.com/assets/578780/3279593/f42363f0-f405-11e3-85cb-eedc178c7b90.png)

I also added a tiny tweak to `FacebookRequests` that tracks the number of requests made to Graph. This is great for debugging. The test suite makes 21 calls to Graph right now FYI. :)

I didn't refactor the tests as much as I wanted to since I didn't want to cause any conflicts with #114. So after that one gets merged, I'll send another PR with a better test refactor. And one goal will be to try and decrease the number of requests made to Graph with each test run. :)