[WIP] Rerun suite after code generation

This probably isn't ready to merge but I'm putting it here for feedback. Automatically reruns the tests after class or method generation

![rerun](https://cloud.githubusercontent.com/assets/237866/4035941/0f38bc18-2c95-11e4-97b8-4f27b1b2f3a2.gif)

To do:

- [x] Initial implementation that works on Unix
- [ ] Check it doesn't explode on other platforms (Windows)
- [ ] Some strategy for testing in Behat (probably will have to run the CLI command rather than ApplicationTester)
- [ ] Some configuration - should it default to on or off?
- [ ] Incorporate #417 and #481 if they get merged