gnome-continuous has multiple processes; the test processes just use ostree_repo_transaction_set_refspec(), but this will end up cleaning out the tmpdir, deleting any temporary files used by the commit process from the build.

We need a more intelligent way to clean up the tmpdir.  Cleaning out files older than a day is a traditional way to do it, but is still theoretically racy.

I think we need to have some way for multiple processes to dynamically synchronize.  Sqlite for example uses a mmapable file.