Track phpspec dev-master

There's loads of stuff in phpspec's master branch that we can use (e.g. namespaced ApplicationTester), and some things that break current functionality (e.g. PSR0 locator fix). I think it'd be good to get develop to follow phpspec for a while like we did prior to phpspec 2.0 so we can start working towards a release to coincide with the next phpspec version.