Clearing out old data

[pmeenan]

I think with a tiny change to allow for "none" or "/dev/null" as the archive location we could make it work out of the box as well without having to hack the script. Only reason it won't work right now is that it verifies that the archive worked before deleting but we could special-case /dev/null and skip the archiving (probably best to have that logic inside archive.inc proper so it also doesn't try to restore).