optimized Event.check_if_cancelled to make zero queries when cancellations are prefetched
optimized Event.check_if_cancelled to make zero queries when cancellations are prefetched

imposeren/django-happenings,wreckage/django-happenings,imposeren/django-happenings,wreckage/django-happenings,wreckage/django-happenings,imposeren/django-happenings