For a given day, and optionally C<month> and C<year> if they are
different from those specified in C<new()>, provide the day of week
-<<<<<<< HEAD
-number. (1=Sunday, 7=Saturday).
-=======
number. (0=Sunday, 6=Saturday).
->>>>>>> upstream/2.04
=item add_days($days, $delta, $day, [$month], [$year])