* objects.h (SCM_SET_ENTITY_SETTER): new macro. SCM_ENTITY_SETTER

* objects.h (SCM_SET_ENTITY_SETTER): new macro.  SCM_ENTITY_SETTER
casts its result, so doesn't yield an lvalue per ANSI C.

* goops.c (s_scm_sys_set_object_setter_x): use
SCM_SET_ENTITY_SETTER.
(clear_method_cache): use SCM_SET_ENTITY_PROCEDURE.

* gc.h (SCM_GC_SET_CARD_BVEC): new macro.  SCM_GC_CARD_BVEC casts
its result, so doesn't yield an lvalue per ANSI C.
(SCM_GC_SET_CARD_FLAGS): ditto for SCM_GC_GET_CARD_FLAGS.
(SCM_GC_CLR_CARD_FLAGS): redefined in terms of
SCM_GC_SET_CARD_FLAGS.
(SCM_GC_SET_CARD_FLAG, SCM_GC_CLR_CARD_FLAGS): ditto.

* gc.c (INIT_CARD): use the explicit setter macro to set the bvec.