Fixed issue #868. Modified assignment.rb graded_submissions method to return only 1 graded submission from each grouping
Fixed issue 728. Uploading an invalid CSV file now shows an error message.
Updated fix to #issue 868 to reflect comments in issue (cleanup)
Merge pull request #1197 from drunkel/issue-868

Fixed issue #868. Assignment.rb graded_submissions method returns only 1 graded submission from each grouping
Added error message if encoding of the uploaded file is incorrect. Improved error message and fixed comment typo.
Merge pull request #1198 from daniyall/issue-728

Fixed issue 728. Uploading an invalid CSV file now shows an error message