def last_modified options = {}
      changed_at = [Time.zone.at(::File.new("#{Rails.root}").mtime), created_at, updated_at, modified_at]
      
      if(options[:include_pages])
        changed_at << Humpyard::Page.select('updated_at').order('updated_at DESC').first.updated_at
      end
      
      (changed_at - [nil]).max.utc    
    end
def last_modified options = {}
      changed_at = [Time.zone.at(::File.new("#{Rails.root}").mtime), created_at, updated_at, modified_at]
      
      if(options[:include_pages])
        changed_at << Humpyard::Page.select('updated_at').order('updated_at DESC').first.updated_at
      end
      
      (changed_at - [nil]).max.utc    
    end
Return the logical modification time for the page, suitable for http caching, generational cache keys, etc.