Added functionality to preserve other versions of the same package when uploading a new package.

Hi Krobertson,

I am going to use your awesome tool to manage our debian packages on S3 but I needed the ability to have several different versions of the same package.

I have added this functionality to your tool as a command line option, but I did not change the default behavior so it won't mess up anyones scripts or tools that rely on deb-s3.

If you like this change or you think it can be useful for others then it would be great if you could pull my changes into the base.

I'm not a ruby programmer so please fell free to give any comments or feedback on my changes.

Best regards,
Peter Csizsek