message: db.file: show s3 upload errors
  Without this commit debugging S3 upload errors is a pain, as there is
  no way to see them.
diff: @@ -232,17 +232,21 @@ pub fn add_path_into_database<P: AsRef<Path>>(conn: &Connection,
  if !futures.is_empty() {
  attempts += 1;
  - if rt.block_on(::futures::future::join_all(futures)).is_ok() {
  + match rt.block_on(::futures::future::join_all(futures)) {
  + Ok(_) => {
  // this batch was successful, start another batch if there are still more files
  batch_size = cmp::min(to_upload.len(), MAX_CONCURRENT_UPLOADS);
  currently_uploading = to_upload.drain(..batch_size).collect();
  attempts = 0;
  - } else {
  + },
  + Err(err) => {
  + error!("failed to upload to s3: {:?}", err);
  // if any futures error, leave `currently_uploading` in tact so that we can retry the batch
  if attempts > 2 {
  panic!("failed to upload 3 times, exiting");
  }
  }
  + }
  } else {
  batch_size = cmp::min(to_upload.len(), MAX_CONCURRENT_UPLOADS);
  currently_uploading = to_upload.drain(..batch_size).collect();
  