This method tells an object to forward the message in the form of an
OM_UPDATE message to all the objects in its broadcast list.  The
modelclass does not map the attributes in these om_update messages.
Because modelclass inherits behavior from icclass, if the model has an
ica_target and ica_map, it will also send a mapped om_update message to
its ICA_TARGET.  The return values for these methods are not explicitly
defined.  See the rootclass om_notify/om_update and icclass
om_notify/om_update descriptions for more information.