rewrite_asset_path

# File actionpack/lib/action_view/helpers/asset_tag_helpers/asset_paths.rb, line 45
        def rewrite_asset_path(source, dir, options = nil)
          source = "/#{dir}/#{source}" unless source[0] == //
          path = config.asset_path

          if path && path.respond_to?(:call)
            return path.call(source)
          elsif path && path.is_a?(String)
            return path % [source]
          end

          asset_id = rails_asset_id(source)
          if asset_id.empty?
            source
          else
            "#{source}?#{asset_id}"
          end
        end