code: public static S3Versions withPrefix(AmazonS3 s3, String bucketName,
              String prefix) {
          S3Versions versions = new S3Versions(s3, bucketName);
          versions.prefix = prefix;
          return versions;
      }
docs: Constructs an iterable that covers the versions in an Amazon S3 bucket
  where the object key begins with the given prefix.
  
  @param s3
  The Amazon S3 client.
  @param bucketName
  The bucket name.
  @param prefix
  The prefix.
  @return An iterator for object version summaries.