ACL support for S3 and Amazon token support

So this addresses two issues I filed ([LIBCLOUD-497](https://issues.apache.org/jira/browse/LIBCLOUD-497), [LIBCLOUD-498](https://issues.apache.org/jira/browse/LIBCLOUD-498)).

The S3 ACL stuff seems solid and has a test, but I couldn't figure out how to write a test for the token code. Any tips?