Add a new relation of the specified type with the specified target to
the current relation set if the relation set does not contain a relation
of that type. If it is does contain a relation of that typea the target
is added to the relation.
Since 1.9
Add a new relation of the specified type with the specified target to the current relation set if the relation set does not contain a relation of that type. If it is does contain a relation of that typea the target is added to the relation. Since 1.9