[youtube] set the 'name' parameter in the subtitles url (fixes #1577)

youtube_dl/extractor/youtube.py

@@ -1116,6 +1116,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor, SubtitlesInfoExtractor):
                 'lang': lang,
                 'v': video_id,
                 'fmt': self._downloader.params.get('subtitlesformat'),
+                'name': l[0],
             })
             url = u'http://www.youtube.com/api/timedtext?' + params
             sub_lang_list[lang] = url