Fix #231: upload_file() fails when file_or_path is open file larger than 5GB and obj_name is specified

The file name (`fname`) was being used as the object name passed to put_object, instead of the object name, `obj_name`. This caused 2 problems:
1) the object name of the uploaded file was not the one the caller asked for
2) the get_object() call at the end of the method failed because it was (correctly) using `obj_name` as the name of the object to get.