add s3-mp-copy.py
fix copying when the size is smaller than multipart threshold
Fix off by 1 error in chunk copying.

The last chunk of the S3 object that was getting copied was not getting copied
if the S3 object was greater than 5GB.
Merge pull request #13 from copiousfreetime/feature/add-s3-mp-copy

Add a parallel COPY for large objects using the MultiPart Upload API