stylesheet_link_tag, javascript_include_tag, caching problems

So, the new caching for stylesheet_link_tag, javascript_include_tag
which rolls up the files into one all.js or all.css files is great ...
however I've run into an issue:

If all.cs or all.js don't exist, they get generated ... great, I've
reduced the number of gets ...

The problem is what occurs when the files already exist ... even if
I've changed my list of js/css files to something completely
different, it won't rewrite the file if it already exists ...

Do we really need the unless in this block? (asset_tag_helper.rb)

        def write_asset_file_contents(joined_asset_path, asset_paths)
          unless file_exist?(joined_asset_path)
            FileUtils.mkdir_p(File.dirname(joined_asset_path))
            File.open(joined_asset_path, "w+") { |cache|
cache.write(join_asset_file_contents(asset_paths)) }
          end
        end