QLocale should support hyphen ('-') separator as specified in ISO 639 and 3166

QLocale today only supports underscore in QLocale::QLocale(QString) and QLocale::name(QString). It should be made to work with '_' as the ISO standard defines; http://www.w3.org/International/articles/language-tags/

First priority is to provide support for parsing with '-' in the locale specification.
Supporting QLocale::name() is less important.