S3 Object Metadata Isn't Populated from Amazon

Based on the current errors, it looks like our API wrapper isn't populating the object metadata, which means that regardless of what kind of comparison we use when trying to decide if we need to update a file during the upload section, we end up always uploading the file.

I think we need to modify our AWS api wrapper to include a method like this:

https://github.com/mitchellh/goamz/blob/master/s3/s3.go#L569