def owner? obj, relation=nil
      if relation     
        return true if user_relation?(obj, relation)
      end                                
      [:user, :owner, :author].each do |relation|        
        return true if user_relation?(obj, relation)
      end
      false
    end
def owner? obj, relation=nil
      if relation     
        return true if user_relation?(obj, relation)
      end                                
      [:user, :owner, :author].each do |relation|        
        return true if user_relation?(obj, relation)
      end
      false
    end
returns true if the current user owns the object
 tries default 'owner' relations if none given as an argument