Refactored file content type discernment from add_datastream and modify_datastream into private method.
Added better support for Rails uploaded files by calling :content_type on file if available.
Added constant for default content type.
Removed Ruby 1.8.7 workaround.
Added tests!
Fixes #61.
Merge pull request #62 from dchandekstark/mimetype-in-add-or-modify-ds

Refactored file content type discernment from add_datastream and modify_...