iso639: lookup fixes and improvements
- Fixes buggy lookup behaviour of mux/ts that got broken in v2.1.
- De-duplicates and simplifies common lookup code.
- Fixes the old ugly hack implementation of 'name-inclusive' searches done by esout,dvdnav,bluray.
- Tweaks the 'name-inclusive' search algorithm to make it work more reliably for ISO-639 code based identifier use in dvdnav/bluray user sub/audio/menu language preferences.