In BindingServices::addInstance, we build the instance only once so we
avoid the cost of rebuilding it at the plugging step.
An additional benefit is that we catch the exception earlier in case of
selfInheritance :
...kernel.InstanciationTest::test007_addInstance_selfInheriting 
and 
...impl.InstanciationTest::testTypeInstanciationWithSelfInheritance)