Force Booking function doesn't move bookings with DST timeshift applied

The force booking function (for people with mrbs:forcebook) doesn't find bookings created before a DST change if trying to forceably book a room after the DST change. This happens because the record stores the time offset by one hour, but the query that searches for clashing bookings doesn't offset the time.
The attached patch amends the query to also search for offset bookings.