test, provide regressions for ywd/ymd conversion
minor, support comparisons of ywd dates
cosmetics, remove #if 0'd code segments
fix, PEBKAC, canonicalise the hang value along with week-count and year
minor, in plain dseq(1) (no -f|--format) stay in the calendar system of the first argument
hygiene, express -1 additively, in terms of the literal GREG_DAYS_P_WEEK
minor, calculate c and w in __make_ywd_ybd() additively
minor, in _ywd_fixup_w() also fix up the hang
Merge branch 'tool/dseq'

* tool/dseq:
  minor, in _ywd_fixup_w() also fix up the hang
  minor, calculate c and w in __make_ywd_ybd() additively
  hygiene, express -1 additively, in terms of the literal GREG_DAYS_P_WEEK
  minor, in plain dseq(1) (no -f|--format) stay in the calendar system of the first argument
  fix, PEBKAC, canonicalise the hang value along with week-count and year
  cosmetics, remove #if 0'd code segments
  minor, support comparisons of ywd dates
  test, provide regressions for ywd/ymd conversion