limn goops flags, remove foreign objs, rename entity to applicable-struct

limn goops flags, remove foreign objs, rename entity to applicable-struct

* libguile/goops.c (scm_class_applicable_struct)
  (scm_class_applicable_struct_with_setter)
  (scm_class_applicable_struct_class): Rename from
  scm_class_entity, scm_class_entity_with_setter, and
  scm_class_entity_class.
  (scm_class_simple_method): Removed; this abstraction is not used.
  (scm_class_foreign_class, scm_class_foreign_object): Remove these,
  they are undocumented and unused. They might come back later.
  (scm_sys_inherit_magic_x): Simply inherit the vtable flags from the
  class's class. Flags are about layout, and it is the class that
  determines the layout of the instance.
  (scm_basic_basic_make_class): Don't bother setting GOOPS_OR_VALID,
  inherit-magic will do that.
  (scm_basic_make_class): Inherit magic after setting the layout. Allows
  the struct magic checker to do its job.
  (scm_accessor_method_slot_definition): Move implementation to Scheme.
  Removes the need for the accessor flag.
  (scm_sys_allocate_instance): Adapt to scm_i_alloc_struct name change,
  and that alloc-struct will handle finalization.
  (scm_compute_applicable_methods): Remove accessor check, as it's
  unnecessary.
  (scm_make): Adapt to new generic slot order, and no more
  simple-method.
  (create_standard_classes): What was the GF slot "dispatch-procedure"
  is now the applicable-struct slot "procedure". No more foreign class,
  foreign object, or simple method. Rename <entity> and friends to
  <applicable-struct> and friends. No more entity-with-setter -- though
  perhaps it will come back too. Instead generic-with-setter is its own
  thing.

* libguile/goops.h (SCM_CLASSF_METACLASS): "A goops class that is a
  vtable" -- no need for a separate flag.
  (SCM_CLASSF_FOREIGN, SCM_CLASSF_SIMPLE_METHOD)
  (SCM_CLASSF_ACCESSOR_METHOD): Removed these unused flags.
  (SCM_ACCESSORP): Removed.
  Renumber generic slots, rename entity classes, and remove the foreign
  class, foreign object, and simple method classes.

* libguile/struct.c (scm_i_struct_inherit_vtable_magic): New function,
  called when making new vtables.applicable structs
  (scm_i_alloc_struct): Remove 8-bit alignment check, as libGC
  guarantees this for us. Handle finalizer registration here.
  (scm_make_struct): Factor some things to scm_i_alloc_struct and
  scm_i_struct_inherit_vtable_magic.
  (scm_make_vtable_vtable): Adapt to scm_i_alloc_struct name change.

* libguile/struct.h (scm_i_alloc_struct): Change name from
  scm_alloc_struct, and make internal.

* module/oop/goops.scm (oop): Don't declare #:replace <class> et al,
  because <class> isn't defined in the core any more.
  (accessor-method-slot-definition): Defined in Scheme now.
  Remove <foreign-object> methods.
  (initialize on <class>): Prep layout before inheriting magic, as in
  scm_basic_make_class.

* module/oop/goops/dispatch.scm (delayed-compile)
  (memoize-effective-method!): Adapt to 'procedure slot name change.