fix mongoid and mongo_mapper incompabilities

lib/impressionist/engine.rb

@@ -10,8 +10,7 @@ module Impressionist
   end
 
   initializer 'impressionist.model' do |app|
-    require_orm
-    ActiveRecord::Base.send(:include, Impressionist::Impressionable)
+    require_and_include_orm
 
   end
 
@@ -27,7 +26,7 @@ module Impressionist
 
 
  private
-  def require_orm
+  def require_and_include_orm
     require "#{root}/app/models/impressionist/impressionable.rb"
     require "impressionist/models/#{orm}/impression.rb"
     require "impressionist/models/#{orm}/impressionist/impressionable.rb"

lib/impressionist/models/active_record/impressionist/impressionable.rb

@@ -1,3 +1,5 @@
+ActiveRecord::Base.send(:include, Impressionist::Impressionable)
+
 module Impressionist
   module Impressionable
     extend ActiveSupport::Concern

lib/impressionist/models/mongo_mapper/impressionist/impressionable.rb

@@ -1,3 +1,5 @@
+MongoMapper::Document.plugin Impressionist::Impressionable
+
 module Impressionist
   module Impressionable
     extend ActiveSupport::Concern

lib/impressionist/models/mongoid/impressionist/impressionable.rb

@@ -1,3 +1,5 @@
+Mongoid::Document.send(:include, Impressionist::Impressionable)
+
 module Impressionist
   module Impressionable
     extend ActiveSupport::Concern