[ec2] treat directory as attribute of files collections

lib/fog/aws/models/s3/files.rb

@@ -8,6 +8,7 @@ module Fog
       class Files < Fog::Collection
 
         attribute :delimiter,     'Delimiter'
+        attribute :directory
         attribute :is_truncated,  'IsTruncated'
         attribute :marker,        'Marker'
         attribute :max_keys,      ['MaxKeys', 'max-keys']
@@ -35,10 +36,6 @@ module Fog
           end
         end
 
-        def directory
-          @directory
-        end
-
         def get(key, options = {}, &block)
           data = connection.get_object(directory.name, key, options, &block)
           file_data = {