Fixed s3 to s3 sync urlencoding pagniation bug.

Keys were not getting url decoded properly with pagination.
If one bucket exited ListObjects pagination before
the other bucket, it caused the handler that decodes the keys
to prematurely exit as well. This resulted in some keys not
getting url decoded.
Merge pull request #909 from kyleknap/sync-encoding

Fixed s3 to s3 sync url decoding pagniation bug.