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.