This method continuously issues OM_NOTIFY messages for each IECLASS_TIMER
event it gets.  The OM_NOTIFY message's OPUF_INTERIM flag (from
opUpdate.opu_Flags) is set for all but the final OM_NOTIFY.

The OM_NOTIFY message contains one attribute/value pair, GA_ID.  If the
pointer is currently over the gadget image, the value of this
attribute/value pair is the gadget's actual GA_ID (from the
Gadget.GadgetID field).  If the pointer isn't over the image, the value is
the negative of the gadget's actual GA_ID.