The added unittest was failing and also x10i. Frontend moves global
entity into class for native method calls. liboo lowering moves it back
during vtable creation.

The issue is that "pmap_insert(map,key,NULL)" does not delete an entry,
so "pmap_contains(map,key)" afterwards does not return false. This
changes add_compound_member to assert a NULL value instead of a NULL
entry.

A similar error might be in ir/be/bechordal.c.