SAK-17219 conversion script update (2.6.1)

SAK-17219 - Getting issue details... STATUS , SAK-1654 - Getting issue details... STATUS : Matt Jones of the University of Michigan reports that the original 2.6.0 to 2.6.1 conversion script that operates on assignment_content table "is inefficient, potentially locks tables and performs too many scans, especially if there are hundreds of thousands of rows." Matt has revised both the MySQL and Oracle conversion scripts to improve their performance.