mark copy_object as idempotent (#706)

closes #704

Author: geemus

lib/fog/aws/requests/storage/copy_object.rb

@@ -34,6 +34,7 @@ def copy_object(source_bucket_name, source_object_name, target_bucket_name, targ
             :headers  => headers,
             :bucket_name => target_bucket_name,
             :object_name => target_object_name,
+            :idempotent => true,
             :method   => 'PUT',
             :parser   => Fog::Parsers::AWS::Storage::CopyObject.new,
           })