Support for plural strings (locale source)

In Drupal plural strings use a Unicode \03 control character as a delimiter for plural forms which is not allowed symbol in XML and XLIFF. Therefore, it's not possible to use the generated file for further uploading into translation systems. Example string: 1 new comment@count new comments - you can find it at /admin/tmgmt/sources/locale/default?label=1%20new%20comment%03%40count%20new%20comments&missing_target_language= page (you may need to add a couple of comments to an article and then view the default front page to expose this string to the locale system).