Function keep_conflict_copy 

fn keep_conflict_copy(
    fs: &FileStore,
    uid: &str,
    dir: &Path,
    dir_id: &str,
    name: &str,
    body: &[u8],
) -> Result<(), StoreError>

Write the other version of a conflicted file beside it and record it, so it follows the agent to its other folders (and a deletion of it, once merged, does too).