bug#26165: date-week-day screws up prior to AD 1

[Zefram]

I wrote:
>written to perform divisions with quotient where it obviously needs
>modulo.

Oops, thinko there.  It needs floor-quotient, the quotient-like function
that uses floor rounding.  modulo is the *remainder*-like function that
uses floor rounding.

-zefram