* recognize subtitles streams in avi. Now to decode them. if anyone has ANY info on how this works :)

(might conflict with HTTP streaming output at a later stage)

* if we find the track name, then store in the fmt.

  - renamed es_out_id_t->psz_description to psz_language to better reflect it's use.
  - Reflect both track name and language (if we know them) in the menu's.