Clean up Testcase and tests.

Cleaned up the current test suite to ensure that all tests are currently
passings and back in the green after the latest refactor.
Fix UploadedFile compatibility issues.

Fixed compatibility issues between the 2.3 version of
Symfony\Component\HttpFoundation\File\UploadedFile (currently used by laravel 4.0)
and the 2.4 version (currently used by Laravel 4.1).  Note: these
problems are arising mainly due to the Symfony team's inability to
decide upon a standard interface for the getErrorMessage method defined
in the UploadedFile class.
Add mockery library for testing.

Added mockery to composer.json.
Improve testability of the attachment class.

Improved the testability of the attachment class:
- Interpolator property is now protected and has accessors/mutators.
- Created getInstanceClass method for returning the class name of the
  attachment's corresponding model instance.
Modify Interpolator to use the getInstanceClass method.

Updated the interpolator class to use the new getInstanceClass method.
Clean up whitespace.

Cleaned up some whitespace and tabbing.
Create Interpolator unit test.

Created unit tests for the Interpolator class.
Make getInstanceClass method public.

Made the getInstanceClass method public so that is callable directly
from the attachment object (should have been like this in the first
place).