Fix overlapping constraint for all-day Occurrences
Fix overlapping constraint for all-day Occurrences

Following various fixes to generation of all-day occurrences we can now
apply the appropriate constraint in the `overlapping` queryset method
to return all-day occurrences on a given day.

ic-labs/django-icekit,ic-labs/django-icekit,ic-labs/icekit-events,ic-labs/django-icekit,ic-labs/icekit-events,ic-labs/icekit-events,ic-labs/django-icekit