UTF-8 encoding problem solved for excel on mac.

There is an encoding problem if you want to open files in excel on a mac. 

http://stackoverflow.com/questions/4348802/how-can-i-output-a-utf-8-csv-in-php-that-excel-will-read-properly

This fix works. You can open it in excel an a mac now too.
Please change to 'exportModificationDate' here and where this variable is used/set