mirror-to-mirror.sh: also sync to ftp.lysator.liu.se, in parallel

This is the deployed script for pushing to the primary mirrors. It starts with the 'repo' section and runs all the rsyncs in parallel to each primary mirror. Once the 'repo' syncs are done, it does the same process for the 'archive' syncs.

This is actually already deployed, but I'd love feedback on this in terms of reliability, etc. since it does change how the old script was operating.