Reintroduce #221

Fixes aws/aws-cli#614.

The fix for botocore was good.  Looking into this issue, the problem was that the accompanying CLI PR was encoding the copy source name to utf-8 when all of that logic is moved into botocore.  This meant that was were utf-8 encoding the source twice, which is what was causing the test failures with unicode chars.

Also see: https://github.com/aws/aws-cli/pull/688