compare week-year not calendar year in compareWeeks

[sahvx655-wq]

compareWeeks reports 31 December and 1 January of the same calendar year as the same week. AbstractCalendarValidator.compare orders the WEEK_OF_YEAR field on Calendar.YEAR and then WEEK_OF_YEAR, but a week belongs to its own week-year, and at the turn of the year that week-year differs from the calendar year. Under the US locale 31 Dec 2018 has WEEK_OF_YEAR 1 and a week-year of 2019, so against 1 Jan 2018 (also WEEK_OF_YEAR 1) the year and the week number both match and two dates roughly 52 weeks apart compare equal. The mirror case fails the other way: 31 Dec 2018 and 1 Jan 2019 share week 1 of week-year 2019 yet compare as different weeks because their calendar years differ.

The fix orders the WEEK_OF_YEAR comparison on the week-year from Calendar.getWeekYear(), falling back to Calendar.YEAR where the calendar does not support week dates, before comparing the week number, and leaves every other field untouched. compareQuarters already shifts its year at the quarter boundary, so this keeps the week comparison consistent with it. The added test fails on the current code and passes with the change.

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