(calendar-week-start-day): New var (autoloaded) to

(calendar-week-start-day): New var (autoloaded) to
allow the calendar week to start on any day, not just Sunday.
(calendar-mod): New support function.
(calendar-cursor-to-visible-date, generate-calendar-month,
calendar-beginning-of-week, calendar-end-of-week):
Use new var calendar-week-start-day.

(calendar-day-name-array, calendar-month-name-array,
calendar-islamic-month-name-array,
calendar-hebrew-month-name-array-common-year,
calendar-hebrew-month-name-array-leap-year):  Change to defvar.