Cleanups

- Drop some copy constructor declarations that we don't need.  Move
  DIE cloning from base to raw/cooked subclasses, cooked DIE's will
  need to have some extra stuff in them.

- Add a bunch of delimiters to better separate value-dw.hh's sections.
Fix op_child_die::operate

- dwarf_child returns a value > 0 for cases where a DIE has no actual
  children even if it's abbrev `haschildren`.  Use our own dwpp_child
  which handles this situation.  This made it possible to simplify the
  code as well.