Finished up webdav, and after running `testremote` for a long time, I'm
satisfied it's good. The newchunks branch has now been merged into master
completely.

Spent the rest of the day beginning to rework the S3 special remote to use
the aws library. This was pretty fiddly; I want to keep all the
configuration exactly the same, so had to do a lot of mapping from hS3
configuration to aws configuration. Also there is some hairy stuff
involving escaping from the ResourceT monad with responses and http
connection managers intact.

Stopped once `initremote` worked. The rest should be pretty easy, although
Internet Archive support is blocked by
<https://github.com/aristidb/aws/issues/119>. This is in the `s3-aws`
branch until it gets usable.
