Refactor test bundle detection

* Moved some headers from the Headers group that were not public
* Started marking public interface in CDRFunctions
* Added optional method to CDRReporter protocol
Add an OS X Test Bundle target
Create separate test scheme for XCTest, Sentest not being linked

Having a separate scheme makes this easier to test because we can actually set it up
how a real user would. It is a little strange to have a test that always fails by design,
but considering how hard this is to unit test, this seems valuable
Add failing target to Rakefile

This tests quite an edgecase, but it is good to have an integration-y test around it