Implement special handling for BObjectList.

- BListValueNode now also handles BObjectLists. In the latter's case
however, it uses the template type parameters to map the array
elements to their actual type. As before, this requires a debug
libbe to function.

Add type handler and corresponding value node for BList.

- When a debugging libbe is present, and a BList is encountered,
we now read its internal structure and expose it as if it were an
array of pointers. Combined with typecasting, this means one can
now easily inspect the content of such a list.