BUG Fix issue with SS_DateTime::FormatFromSettings failing to parse dates

Fixes regression from https://github.com/silverstripe/silverstripe-framework/commit/26f8341438bc4f9e31777e8e5c4cc6b556dea1b0 where dates would sometimes fail to parse, but only those from certain times of the month. April fools indeed...

This is resolved by passing Zend_Date the internally used format specifier when parsing a date value.

Future test cases covering date or time should probably consider date values that still validate with interchanged day and month values.