[hacc] Try implementing GetSet*::collapse
[hacc] Test collapsing.  There's one failing test.
[hacc] Don't fail when missing collapsed attr name.
[hacc] Fix some collapse bugs
[hacc] Ignore unused attrs, hopefully fixing a bug in collapsed attrs
[hacc] Fix collapse bug during prepare and finish
[phys various] Rename Object::def to bdf
[ent] Use collapsed attrs in ROD and Biped
[hacc] Fix bug with collapse attrs and foreach_address and foreach_pointer
[various] Make full use of collapsed attrs