Add absolute_path to File class.
Make absolute_path method a class method.
Make absolute_path respect original method's signature.
Code cleanup.
Make absolute_path method available only for Ruby version 1.9.1 or above.
Update absolute_path to use the fake file system's working directory.
Fix absolute_path spec.
Merge branch 'add_absolute_path'

* add_absolute_path:
  Fix absolute_path spec.
  Update absolute_path to use the fake file system's working directory.
  Make absolute_path method available only for Ruby version 1.9.1 or above.
  Code cleanup.
  Make absolute_path respect original method's signature.
  Make absolute_path method a class method.
  Add absolute_path to File class.