Patches written by John Layt to:

1) Add some new methods to KCalendarClass API to match QDate4, to support proper date range validation, and help app programmers implement their own calendar systems.

2) Change the date range limits hard-coded into KCalendarSystem to match QDate4 or each calendars epoch, as appropriate.

3) Clean up the KCalendarSystem implementations to be simpler, more consistant, and to share more code (and add unit tests!)

4) Modify KDateWidget, KDateTable and KDatePicker API (& BIC?) to allow multiple calender systems to be displayed at the same time, as well as do code clean-up.