o.c.ui.util.ComboHistoryHelper: Allow reacting to every selection

Before, only a _different_ selection was sent. Re-selecting the same
item was ignored. Now either one is possible.
o.c.alarm.beast.ui.table: PV filter didn't allow re-selection

When trying to use the same filter with a different set of alarms, this
didn't work because o.c.ui.util.ComboHistoryHelper didn't send an event.