Ramdisks and hard drives as cache devices

> (Reliable, crash resistant)

That's what I've been working towards :)

Safe write behind caching really is a large step up in terms of the guarantees the cache has to be able to make - with writethrough caching, you just have to make sure you return good data, or nothing. And btree code is hard enough, so I've been working on getting the easy cases rock solid first - but safe write behind caching is absolutely happening. I've got some of the preliminary stuff out of the way and I'm hoping to have a rough initial version before too long, depending on how debugging the new stuff goes.