Fixed an issue where accessing a queue across regions generated a signature error.

Fixes #508
When adding a custom delivery method, need to use AWS::Rails namespace
Add Header Options to AWS::S3::Client#head_object

The #head_object operation is supposed to parallel the #get_object
operation for all input headers, but this was not the case due to an
omission in the hand coding. This change adds the remaining input
headers and the associated test.

Resolves issue #495.