* all: added a --audio-language and --spu-language to select tracks based
on language code.
Both options accepts a list (comma separated) of country code(2/3 letters)
or name (english/native).
For demuxers that doesn't provide language info, they are ignored.
Support for dvdnav isn't complete (only first language is tried) and untested.
Ex: --spu-language en,fr will try to select english track and if none
then french one (and if none, no subtitle).
(you can also use --spu-language english,french or english,francais)