Object server-side encryption

[gaul]

Lack of support prevents some kinds of testing, e.g., s3fs integration tests with -o use_sse. Full support for this requires jclouds work like apache/jclouds#130. Is there some shortcut here instead of implementing a few providers and the portable abstraction? Perhaps just passing through the S3 headers? I notice that https://github.com/jiffysrc/s3proxy/commit/fc8547fb52c4013712760ee93b648d469fea5035 has some partial support. @jiffysrc