Duplicate a course multiple times.

In working on integration with an external student database for a Catalyst client, I needed to take a template course and make multiple copies of it.
The current duplicate_course function works by making a backup of a course and restoring it into the new course. This patch seeks to streamline the process a little for multiple courses by doing one backup and multiple restores from that backup.
It looks like there is still much room for improvement - doing 1100 copies of an empty template took just over 2 hours on my development machine, with later copies taking much longer than earlier ones (O(n^2) algo somewhere?). If I find time, I'll try to see what can be done to improve things further.