a very big commit cleaning up structs & goops. also applicable structs.

a very big commit cleaning up structs & goops. also applicable structs.

I tried to split this one, and I know it's a bit disruptive, but this
stuff really is one big cobweb. So instead we'll pretend like these are
separate commits, by separating the changelog.

Applicable struct runtime support.

* libguile/debug.c (scm_procedure_source):
* libguile/eval.c (scm_trampoline_0, scm_trampoline_1)
  (scm_trampoline_2):
* libguile/eval.i.c (CEVAL):
* libguile/goops.c (scm_class_of):
* libguile/procprop.c (scm_i_procedure_arity):
* libguile/procs.c (scm_procedure_p, scm_procedure, scm_setter): Allow
  for applicable structs. Whee!

* libguile/deprecated.h (scm_vtable_index_vtable): Define as a synonym
  for scm_vtable_index_self.
  (scm_vtable_index_printer): Alias scm_vtable_index_instance_printer.
  (scm_struct_i_free): Alias scm_vtable_index_instance_finalize.
  (scm_struct_i_flags): Alias scm_vtable_index_flags.
  (SCM_STRUCTF_FLAGS): Be a -1 mask, we have a whole word now.
  (SCM_SET_VTABLE_DESTRUCTOR): Implement by hand.

Hidden slots.

* libguile/struct.c (scm_make_struct_layout): Add support for "hidden"
  fields, writable fields that are not visible to make-struct. This
  allows us to add fields to vtables and not break existing make-struct
  invocations.
  (scm_struct_ref, scm_struct_set_x): Always get struct length from the
  vtable. Support hidden fields.

* libguile/goops.c (scm_class_hidden, scm_class_protected_hidden): New
  slot classes, to correspond to the new vtable slots.
  (scm_sys_prep_layout_x): Turn hidden slots into 'h'.
  (build_class_class_slots): Reorder the class slots to account for
  vtable fields coming out of negative-land, for name as a vtable slot,
  and for hidden fields.
  (create_standard_classes): Define <hidden-slot> and
  <protected-hidden-slot>.

Clean up struct.h.

* libguile/struct.h: Lay things out cleaner. There are no more hidden
  (negative) words. Names are nicer. The exposition is nicer. But the
  basics are the same. The incompatibilities are that <vtable> has more
  slots now, and that scm_alloc_struct's signature has changed. The
  former is ameliorated by the "hidden" slots mentioned before, and the
  latter, well, it was always a very internal thing...
  (scm_t_struct_finalize): New type, a finalizer function to be run when
  instances of a vtable are collected.
  (scm_t_struct_free): Removed, structs' data is managed by the GC now,
  and not freed by vtable functions.

* libguile/struct.c: (scm_vtable_p): Now we keep flags on
  vtable-vtables, so this check is cheaper.
  (scm_alloc_struct): No hidden words. Yippee.
  (struct_finalizer_trampoline): Entersify.
  (scm_make_struct): No need to babysit extra words, though now we have
  to babysit flags. Propagate the vtable, applicable, and setter flags
  appropriately.
  (scm_make_vtable_vtable): Update for new simplicity.
  (scm_print_struct): A better printer.
  (scm_init_struct): Define <applicable-struct-vtable>, a magical vtable
  like CL's funcallable-standard-class. Also define
  <applicable-struct-with-setter-vtable>.

Remove foreign object implementation.

* libguile/goops.h:
* libguile/goops.c (scm_make_foreign_object, scm_make_class)
  (scm_add_slot, scm_wrap_object, scm_wrap_component): Remove, these
  were undocumented and unworking.

Clean up goops.h, a little.

* libguile/goops.h:
* libguile/goops.c: Also clean up.
* module/oop/goops/dispatch.scm (hashset-index): Adapt for new hashset
  index.