Fragment scope. Works and passes all tests.

Work on  https://github.com/roboguice/roboguice/issues/146

TODO inner fragments. It would be very nice if the injector of an inner fragment could be a child injector of its parent. This looks logical. Nevertheless, it looks like there is no way to know the parent Fragment of a subFragment before API 17.

http://developer.android.com/reference/android/app/Fragment.html#getParentFragment()