- scriptified the remains of APowerup.

- ensure that actor defaults contain a valid virtual table and class pointer so that they can actually use virtual and class-dependent method functions. This is needed for retrieving script variables from them.

src/dobject.cpp

@@ -275,6 +275,7 @@ DObject::DObject ()
 {
 	ObjectFlags = GC::CurrentWhite & OF_WhiteBits;
 	ObjNext = GC::Root;
+	GCNext = nullptr;
 	GC::Root = this;
 }
 
@@ -283,6 +284,7 @@ DObject::DObject (PClass *inClass)
 {
 	ObjectFlags = GC::CurrentWhite & OF_WhiteBits;
 	ObjNext = GC::Root;
+	GCNext = nullptr;
 	GC::Root = this;
 }