rbx-require-relative

Ruby 1.9's require_relative for Rubinius and MRI 1.8. We also add abs_path which is like __FILE__ but __FILE__ can be fooled by a sneaky "chdir" while abs_path can't. If you are running on Ruby 1.9 or greater, require_relative is the pre-defined version. The benefit we provide in this situation by this package is the ability to write the same require_relative sequence in Rubinius 1.8 and Ruby 1.9.