Added relation redaction logic, same as node and way logic, plus tests

app/models/old_relation.rb

@@ -1,10 +1,13 @@
 class OldRelation < ActiveRecord::Base
   include ConsistencyValidations
-  include Redactable
   
   self.table_name = "relations"
   self.primary_keys = "relation_id", "version"
 
+  # note this needs to be included after the table name changes, or
+  # the queries generated by Redactable will use the wrong table name.
+  include Redactable
+
   belongs_to :changeset
   belongs_to :redaction
   belongs_to :current_relation, :class_name => "Relation", :foreign_key => "relation_id"