Fixed order of prefectures select (ISO 3166-2:JP).
 Fixed first elements of JP_PREFECTURES to code of prefecture (ISO 3166-2:JP).
Fixed tests to correspond to ISO 3166-2:JP.
Added the old version of JP_PREFECTURES for conpability.
Changed JP_PREFECTURES to JP_PREFECTURE_CODES as the code of prefecture

The fixing first elements of JP_PREFECRUES to some another value (in change set `67c9ae7`)
will break backward compatibility.

So, Added the choices as another value named JP_PREFECTURE_CODES
and JPPrefecturCodeSelect as it's form.
Merge pull request #27 from hirokiky/iso3166-2

Fixed JP_PREFECTURES to conform to ISO 3166-2:JP.