Started building import tree (in the importtree branch). So far the content identifier storage in the git-annex branch is done. Since the API tells me it will need to both map from a key to content identifiers, and from content identifier to the key, I also added a sqlite database to handle the latter.

While implementing that, I happened to notice a bug in storage of metadata that contains newlines; internals said that would be base64'd, but it was not. That bug turns out to have been introduced by the ByteString conversion in January, and it's the second bug caused by that conversion. The other one broke git-annex on Windows, which was fixed by a release yesterday.