allow non_versioned_columns to be passed in as an option

lib/acts_as_versioned.rb

@@ -185,7 +185,7 @@ def acts_as_versioned(options = {}, &extension)
           self.version_sequence_name        = options[:sequence_name]
           self.max_version_limit            = options[:limit].to_i
           self.version_condition            = options[:if] || true
-          self.non_versioned_columns        = [self.primary_key, inheritance_column, 'version', 'lock_version', versioned_inheritance_column, 'created_at', 'created_on']
+          self.non_versioned_columns        = [self.primary_key, inheritance_column, self.version_column, 'lock_version', versioned_inheritance_column, 'created_at', 'created_on'] + options[:non_versioned_columns].to_a.map(&:to_s)
           self.version_association_options  = {
                                                 :class_name  => "#{self.to_s}::#{versioned_class_name}",
                                                 :foreign_key => versioned_foreign_key,