We weren't installing the headers, but at the moment all symbols
starting with ostree_ were being exported. Fix that by prefixing
non-static symbols with '_'.
https://bugzilla.gnome.org/show_bug.cgi?id=731369
We really want the ability to take a .tar.gz and directly import
it into a repository, without creating a temporary filesystem tree.
First, doing it this way is significantly faster. Also, this allows
us to handle importing tar files with e.g. uid 0 files into packed
repositories as non-root, which is very useful for tests and builds.