[LangCodeExpander] Add method CompareLanguages(const CStdString& lang1, const CStdString& lang2).
Its purpose is to determine if two languages strings given as ISO 639-1, ISO 639-2/T, ISO 639-2/B codes, or english language names represent the same language.
[DVD/OMXPlayer] Fix auto-selection of audio and subtitle streams by using a generic language compare method.
XBMC's audio and subtitle language is stored as an ISO 639-2 T code, but a video's metadata could also store it as an ISO 639-2 B code which could differ from the T variant.