nth_kday_to_jd

# File lib/date.rb, line 479
    def nth_kday_to_jd(y, m, n, k, sg=GREGORIAN) # :nodoc:
      j = if n > 0
            find_fdom(y, m, sg) - 1
          else
            find_ldom(y, m, sg) + 7
          end
      (j - (((j - k) + 1) % 7)) + 7 * n
    end