Don't exit the gradle process after cucumber finishes

This should fix issue #14.

* I bumped the cucumber version to 1.1.6, as there are some differences in the code called between 1.1.5 and 1.1.6.
* I also moved the classloader saving / restoring to be more closely around the code that calls cucumber - it felt weird to save the classloader to the thread context and then pass it in to there as well (as we have to to call the Runtime API directly).
* There's a cucumber test that you can run a gradle task after cucumber which fails without this patch.