more care regarding SCM_PACK and SCM_UNPACK

more care regarding SCM_PACK and SCM_UNPACK

* libguile/control.c (reify_partial_continuation):
* libguile/eval.c (RETURN_BOOT_CLOSURE):
* libguile/frames.c (scm_frame_num_locals, scm_frame_local_ref)
  (scm_frame_local_set_x)
* libguile/frames.h (SCM_FRAME_SET_RETURN_ADDRESS):
  (SCM_FRAME_SET_MV_RETURN_ADDRESS, SCM_FRAME_SET_DYNAMIC_LINK):
* libguile/goops.c (scm_class_of, scm_primitive_generic_generic)
  (scm_c_extend_primitive_generic, compute_getters_n_setters)
  (scm_sys_initialize_object):
* libguile/guardians.c (finalize_guarded):
* libguile/list.c (SCM_I_CONS):
* libguile/macros.c (scm_i_make_primitive_macro)
  (scm_make_syntax_transformer):
* libguile/memoize.c (MAKMEMO, SCM_MAKE_MEMOIZER)
  (SCM_MAKE_REST_MEMOIZER):
* libguile/modules.c (scm_module_reverse_lookup)
* libguile/print.c (iprin1):
* libguile/promises.c (scm_make_promise)
* libguile/srcprop.c (scm_make_srcprops):
* libguile/vectors.c (scm_c_vector_ref):
* libguile/vm-engine.c (vm_engine)
* libguile/vm-i-scheme.c (REL, add1, sub1):
* libguile/vm-i-system.c (new_frame, call_cc)
* libguile/weaks.h (SCM_WEAK_PAIR_WORD_DELETED_P): Be more careful about
  SCM_PACK / SCM_UNPACK.