parse_locale(): upper-case variant tag to match file system

[akx]

Upper-casing the variant tag should be okay, since quoth the spec:

At all times, language tags and their subtags, including private use
and extensions, are to be treated as case insensitive: there exist
conventions for the capitalization of some of the subtags, but these
MUST NOT be taken to carry meaning.

Fixes #814

[akx]

@krassowski Does this look like a good approach to you?

[krassowski]

Thank you, this would fix my issue. Is it guaranteed that future version of CLDR will follow the same naming (using capitals?).

For even better UX (preserving the capitalisation) one could consider rewriting the load() method to read the list of files in the locale-data directory first and then find the appropriate casing of the relevant .dat file (but I am not sure if it is worth the effort).

[akx]

I'd imagine they won't change the casing anytime soon - maybe I should add a check for that in #826 anyway.

The loading code will need reworking later anyway (there are nebulous plans for a "Loader" interface in Babel 3, whenever that is).