Robolectric 2.3 support without any Robolectric modifications

This branch pulls up all the private logic from RobolectricTestRunner into BurstRobolectricRunner.  Unfortunately, it's only compatible with Robolectric 2.3 right now, but with some minor changes to Robolectric (next major version) we could easily remove most of the logic from BurstRobolectricRunner.
It's a required tag in the specification. Certain things will fail without it so we just always include an empty one now.