aggregate clone vtable

[Leopold Toetsch]

- Array, PerlArray, Hash, PerlHash clone is a deep copy
- {Fixed,Resizable}PMCArray is a shallow copy
The deep copy of Array and Hash breaks (infinite recursion) with 
self-referential structures.

I think the deep copy should be a shallow copy.
Deep copy can always be done in a safe way by freeze/thaw.
leo