Added logic to DataMapper::Model#append_inclusions to add inclusions …

…to all existing Model descendants. All in-memory specs pass.

lib/dm-core/model.rb

@@ -86,6 +86,10 @@ def self.descendants
     # @api semipublic
     def self.append_inclusions(*inclusions)
       extra_inclusions.concat inclusions
+      # Add the inclusion to existing descendants
+      self.descendants.each do |model|
+        inclusions.each {|inclusion| model.send :include, inclusion }
+      end
       true
     end