Preferably order page revisions by version

Unordered versions would cause some mess. We need to make sure the versions are sent ordered for things to work well, at the cost of dates being in the wrong order.

We sort by versions, and if we can't to that because of a missing version or because a version doesn't follow a pattern we can understand (digit(\.digit)*), we order by dates and rewrite the versions.

(note that we haven't actually noticed discrepancies between version order and date order, just that it's more sound like this)