Use rsync for transfering files

This seems like a nicer way to do it. rsync is told to copy everything except pipes, sockets (used for IPC; everything needed will be constructed on next boot anyway), and devices (save for hackers playing around, those are confined to /dev anyway). Some directories are justifiably omitted, everything is transfered as-is, more reliably and in half the time.

This is yet untested as I'm waiting for my live jessie to come out of the "kitchen" (live-systems custom build service). It's been almost two days now. :worried: