"Warning: Redefining inherited variable" when starting Roxen

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=2638

Reported by Martin Nilsson, IDA nilsson@pike.ida.liu.se

The following is printed out when Roxen 2.4 is started

/export/d1/nilsson/pike/7.3.13/lib/modules/Calendar.pmod/YMD.pmod:1929:
Warning: Redefining inherited variable 'Day' with different type.