Andrew Ruthven a323ba8dae Don't change the day of the month to 28, if it is > 28
Gosh. The logic was saying, if the modified date has a day of the
month > 28, change it to 28. Which is rather odd. Don't do that.

This closes #248. It also fixes a bug with FREQ=MONTHLY;BYMONTHDAY=-1
as it turns out.
2022-12-18 13:52:48 +13:00
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2022-12-15 15:09:17 +13:00