GOOPS: Deprecate "using-class" procs like slot-ref-using-class

GOOPS: Deprecate "using-class" procs like slot-ref-using-class

* libguile/deprecated.h:
* libguile/goops.c:
* libguile/goops.h:
* libguile/deprecated.c (scm_slot_ref_using_class):
  (scm_slot_set_using_class_x):
  (scm_slot_bound_using_class_p):
  (scm_slot_exists_using_class_p): Deprecate.

* module/oop/goops.scm (slot-ref-using-class, slot-set-using-class!)
  (slot-bound-using-class?, slot-exists-using-class?): Deprecate.
  Change to check that `class' is indeed the class of `obj', as
  required, and then dispatch to slot-ref et al.