Hrm. This means you can't use appcache without autoupdate too. Feels a little odd, as I would expect them to be somewhat orthogonal in terms of impact on an app. Seems like if we want to allow manual or auto updates, it should work whether or not your app is cached.

Maybe appcache should duplicate the hash computation code, rather than try to share with autoupdate? I mean, arguably, the appcache manifest _shouldn't_ depend on the autoupdate environment variables, etc. Not sure here.