Even if very suboptimally, for now; we copy the files, then copy them
again.
The obvious long term plan is to merge pull-local and pull together,
but truly optimizing that requires the pull code to know how to use
the OstreeRepo APIs when operating on local repositories (as
pull-local does), rather than assuming the remote is an archive-z
fetched over HTTP.
This is where loose content objects are stored as one compressed file,
instead of the two separate ones for regular archive mode. This mode
would be suitable for HTTP servers, beause only one HTTP request is
necessary, and the result would be compressed.
Colin Walters